I used to race a stock-class FWD car that had a sub-frame. I “blue-printed” its location to the millimeter for perfect squareness and side-to-side position. It took a full day of string-lining and prying to get it right with the engine and suspension in place. Another couple hours to re-do the 4-wheel alignment on the garage floor with string-lines. I saw cross-eyed for 2 days after!
Drilling alignment holes so you can put in 2 punches at 2 corners when you re-install can help get it exactly back to the right spot. We found it just as easy to pull the engine and trans out as a unit than drop the subframe to change a clutch. I had a cherry-picker but no lift and it didn’t need an alignment after.
I think the tire barn guy is worried something bad is going to happen when he tries to loosen the subframe bolts, in order to shift it over
To be more exact, he’s probably worried the bolts are rusted in place, or maybe they’ll break, etc.
It’s normal to charge more to shift the subframe, and it’s impossible for him to give you an exact quote at first, because he doesn’t know what shape the bolts are in, before hanging a wrench on them
I would look for an independent shop that specializes in alignments and front end work. They’ll be able to do a 4 wheel alignment, and if that includes shifting the subframe to get the job done, that’s probably routine work for them
The tire barn guy may not even be used to that kind of work