Price doesn't sound terrible providing it has a negotiable title (in other words title isn't messed up by someone signing it and not transferring, or anything that would require extra work to get the title moved over.)
Swapping a regular cab isn't too difficult if you have some basic equipment. If it's an extended cab you'll probably want easy access to a 2-post lift.
I've done a couple regular cabs - one with a chain hoist and strap, and another with an engine hoist, chains, and engine load leveler. The engine hoist was more work but not too bad; the chain hoist and strap we got into a little bit of a hurry and didn't realize the strap mashed the little rail flat where the door opening weatherstrip attaches. Not too bad to gently hammer it back in shape, just something to watch out for.
This one had to be swapped because someone really screwed up the job of the interior "update" swap and had butchered the sheetmetal around the steering column support. Black cab was a '94 C1500 5.7; gold replacement cab was an '89 C1500 5.7, with clean title.
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Then my '94 3500HD which didn't actually get swapped, but I did take it 100% apart and pulled the cab off the frame so I could POR-15 everything. For the mount points on the chains, I used the bolt holes for the front cab mounts, and seatbelt retractors:
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Richard