Few collision shops will take this on, for several reasons....main ones being time involved to do it right, interruption of normal workflow, and forgive me, this is not aimed at anyone in particular, people with old cars tend to be cheapskates on this kind of stuff. I can't see anyone doing it for less than 5 hrs/"labor units" a side if they're going to do it right. With a door rate of $55/hr frame labor, that's $550. My cut of that as a tech is going to be in the ballpark of $180-$225, depending on how well I negotiated my pay rate. It'll take at least all day to do it, if I know what I'm doing...because remember, I am going to have to stand behind my work, so I'll be setting up and measuring the car, dealing with 30 year old rusty body mounts, lowering the frame ...you DID want it welded on ALL 4 sides, right?, cutting, welding, grinding, priming, painting, and reassembling .
OR
I can install a new bedside on a late model truck for the same hours/money in half a day.
A lot of people in the trade are car guys, but it's a big difference between what it takes to do it casually for yourself or a buddy and making a living at it.
Personally, if I had it to do all over again, I'd hire a bunch of roofing crews and watch the cash roll in. Back when i was a young pup, I worked construction. ALL the roofers drove the most used-up old beater trucks I have ever seen. You always wondered if they would actually show on time or make it back from lunch. Now all I see are 4x4 supercab turbo diesels driven by the foremen and estimators, and late model CCDs by the crews, pulling spendy dump trailers. Our old roofer had a 1953 F600 with an even more decrepit looking dump bed to haul off the debris in....and this was in 1980.
Now, I'm sure there are roofers that ado not fit the above profile....you see, life isn't really as simple as the generally-held opinions about ANY given group of people or trade.