Just had this happen to me while leaving for a friend’s house, my rear coil burst through its lower footing. Thankfully it was just a block from my own place. The entire undercarriage is rusted and I’m wondering how much I’d have to put into it to make it drivable again.
I appreciate your insight
When that happened to my sons Buick, I welded in fabricated spring perches.
Tester
When rust becomes excessive, and it sounds like now it is excessive, there is no economical repair. It is much cheaper to junk the car and buy a different used car with no rust.
Unless you have a friend like tester good with a welder and fabrication, or yourself, plus a lift to make it easier, I’m afraid you are into several thousand from a shop. I think it is end of the road for not your fathers Buick.
Another vote to just replace this vehicle since rust never sleeps and you only see a small portion of it . I would doubt if any body shop would even want to do this without a large deposit before they even start.
+1
I would doubt the integrity of a body shop claiming that they could properly remediate widespread chassis rust damage on a 23 year old vehicle.
(Translation=Time to drive it to the junk yard and start looking for another vehicle that isn’t severely damaged by rust.)
Ask your shop or a well-recommended body shop to assess the car’s rust situation. A car’s underside can look to be riddled by rust, but other than a couple of spots, it is only surface rust. On the other hand the surface rust can appear to be fine, but careful inspection shows rust is penetrating the car’s structural parts to such an extent it is not economical to repair.
In other words, don’t guess, decide how to proceed based on an expert’s opinion , someone who’s actually seen your car.
That is true, but when chassis rust gets to the point of a rear spring bursting through the “footing”, that means the rust damage is severe.
That “footing” is more than merely a floor panel, and I hope the OP realizes that the structural integrity of his car’s unibody structure is now seriously compromised. While it might be possible for a body shop to do the extensive repairs that are probably needed, I doubt that those repairs could be done for less than the book value of this old car.
The sons spring perches rusted because dirt/debris sat in the perches causing them to rust.
These perches are just stamped out sheet medal.
All the other steel just had surface rust because it was made of heavier steel.
Company’s sell replacement spring perches to be welded in.
But no one had them available for his car.
So I fabricated them.
Tester
@Sarcastro
I like George_San_Jose’s recommendation.
As others have noted, it could be the end the vehicle’s life. But I’ve had some success with a close friend welding some stiff supports over a badly rusted frame. It lasted for years.
How about posting some pictures?
Thanks everyone for the insights. I’ll post pics in the morning 
Thanks for the pictures
Looks like the rear lower control arms have rusted out
That rusted out muffler also caught my eye
Besides the muffler and rust . . . does the car still run well?
Needless to say, this is a very bad time to be shopping for any car, used or new
And I’m not making any guesses about your financial situation, as it’s not my business
Any chance you can locate cheap new rear lower control arms . . . or at least used arms in decent shape?
I did a quick google search and nothing really came up . . . but I didn’t look on ebay
She runs super well, a little on the noisy side b/c of the muffler but other than that pretty good for the $2400 I paid a little over a month ago; 110k miles and good gas milage.
Any idea on a reasonable ballpark on parts and labor?
I’m guessing an afternoon to fix the rear suspension . . . are you planning to fix this yourself?
Normally, it would be a pretty quick job to replace 2 lower control arms, but the rust complicates things. I anticipate lots of penetrant and a torch being used to heat up things, and hoping nothing else breaks that isn’t already broken. That said, I suspect all the control arm nuts and bolts will have to be replaced. The springs look kind of deformed, but they might turn out to be okay once you have them all the way out.
I think you want an effective repair as cheap as possible
Is the front suspension in the same condition?
This has the 3.8-liter V-6, correct?
Any pick-a-part junkyards in your area?
If not, you should consider calling some junkyards and telling them what parts you’re looking for . . . maybe they can locate them
I have a feeling if you need good used control arms, they might be located out-of-state, in the southwest.
What kind of inspections do they have in your area?
Safety?
Emissions?
The exhaust repair should be fairly routine for a decent muffler shop
Thanks for the tips.
I don’t have the tools to do this on my own but getting the parts together my would definitely reduce the cost of repairs.
I’m guessing of with a competent mechanic this would be 4-6hrs max?
You got the engine right and she purrs like a kitten 
. There’s a U-Pull-It in my area that I’m going to check out.
That’s an interesting idea about looking for parts from the south, I’ll take a look into that.
Most shops do not want you bringing them the parts . A very good chance that you will bring some that are not needed or they have to source more parts. 4 to 6 hours not likely . More like a week at least. Back to what others have said , pay to have this thing looked at and then decide if it is worth the cost.
I’ll be blunt . . .
If you want to keep this 23yr-old Buick running for a few more years without breaking the bank, I highly suggest you buy a Chilton manual . . . or a CD-rom or whatever . . . and start acquiring the tools and knowledge to do a lot of the repairs and maintenance yourself
ANY older car needs lots of repair and routine maintenance every single year
If you intend to pay a shop to repair it, you’ll need to get that car towed to a shop. Call around and tell them what your situation is; I’m guessing some of the shops will decline right over the phone, based on possible problems even sourcing the parts.
But if/when you do bring the car to a shop, expect it to stay there for quite awhile. It may not be their priority, because first they’ll have to decide if they can or even want to attempt a repair. And then they have to actually obtain the parts. And if the shop does source used parts, they may not give you any kind of guarantee on the repair.
And also be prepared for a shop to look at the car and say they won’t do it and you should retire the car.
Do you at least have a decent jack and jack stands?
If so, it might be good to post pictures of the entire underneath of the car and post them here. The pictures might influence any further comments we make
