Count on $200-300 on jack stands, and other tools. I’d get it done by a shop, as others have mentioned.
I figure I can change the entire system in less time than it’ll take me to drive to and wait at a shop. The hundred bucks or so it’d cost me in tools if I didn’t already have them would easily be offset by what the shop would charge for their time and labor.
Besides, the original question was simply whether or not we felt her BF could do the job. 
Tell your boyfriend to go for it.
While there is no mention of the BF’s age, I do remember back when I was young and eager to personally tackle every job I could. Even the ones that got me in over my head.
Did I screw up a few of them? Sure. But that’s where I learned the most.
Thank you to everyone for the advice; I really appreciate it. The bf reassured me that he’s worked on exhaust systems before, so we’ll take a look at the situation and if it’s too rusty may still take it to a shop, but otherwise give it a go. I really appreciated having some knowledgeable outside input!
@db4690 In addition to the loud noise, the OP reported: “It also felt like it had trouble accelerating when I would try to get going after a stop”.
I understand a plugged cat can cause a performance problem but if you have a loud exhaust noise that would suggest a rusted out and leaking cat which would not likely also cause a power loss problem. The two symptoms seem to be inconsistent unless the cat got plugged first and then the cat fell apart. That was the only curious part of the symptoms reported. Possible though that the loss of power was an illusion though.
It’s extremely helpful to have 6 point sockets or 6 point box wrenches to avoid rounding off the bolt heads & nuts. He might have to tap them on with a hammer to break through the rust.
soak the hardware with penetrant well ahead of time
BF here, parts are on order and will arrive in the next week or so. I appreciate all of the suggestions!
The catalytic converter needs to be replaced regardless of whether it’s the cause of the performance issue, unfortunately. The rear flange on the converter is severely corroded and there are a lot of “if” statements involved in making it work with a new resonator pipe. The flange of the old resonator pipe is still on there for one (the pipe split near the weld for the flange), and the bolts still there have been rusted round (ie, no more threads). I think I’d have to cut them and then try to hammer them out (with a mallet and punch), but I don’t have an oxy-acetylene setup with me, so I’m not optimistic about that approach. I’ll take a closer look at it once I get the converter off. If it looks more doable then…we’ll see.
Interestingly, the bolts on the front of the converter aren’t rusted nearly as bad. I used a metal brush to get some of the rust off and everything underneath still looks sharp and shiny. I couldn’t get them off yet, but we’re going to grab some rust penetrant later and work them then. Worst case, I’ll grab a pipe and cheat them off. I’m a bit worried about the angle I’d be working at there, so I’m going to try and brace the converter from underneath with a wood block. I don’t want to ruin the connection to the front exhaust pipe.
I’m a bit concerned about the oxygen sensor, which looks pretty rusted into the old resonator pipe. I’ll look at it more closely tomorrow/tonight.
Cost breakdown so far:
~$80 – two 4-ton jack stands, two wheel chocks, safety goggles, nitrite gloves, and a 6-ton bottle jack (I had to exchange the jack this morning, one of the internal seals broke almost immediately when I first used it).
~$170 – new converter and resonator pipe
$10-20? – pb blaster or something (tonight)
Total: $270
Time investment so far: approx. 4 hours (including buying things, research, and jacking up the car)
My relevant auto/mechanical experience: I worked as an assistant mechanic on a ranch in California for three years. I’ve worked on cars/tractors/balers/etc… (mostly models from the 60s to the early 00s).
Oh, and the car’s loud because the resonator pipe is split – so the exhaust is coming straight out of the catalytic converter at this point. The shop just zip-tied the resonator pipe off to the side. I suspect that the acceleration problem was a slow onset issue that was made more obvious once the car sounded like a dirt bike whenever the accelerator was tapped.
Most mechanics don’t even bother trying to remove the old bolts. Just cut 'em and move on with the job. Nuts and bolts are too cheap to bother with.