"...the price of a nice body. Have you priced any nice...bodys lately?..."
Yeah, that will definitely be a factor in deciding what combo to use.
That's the problem with running a '69 GTO. Any clean '64-'72 GTO body is going to be really high.
As for running a '77 combo. I don't know what non-Bird body would be the the cheapest, & easiest to find. I'm guessing maybe a GP. Most everything except GP's & Birds have probably long since been crushed, because of a lack of interest.
Just for kicks, I'm gonna Google & see what I can find that looks decent enuff to possibly build a Stocker with. Will edit & add to this post as I find 'em. Might be interesting.
If I were serious about building a Pontiac Stocker, I'd contact several of the active Pontiac racers, such as Bob Michael. I figure most long time class racers are always looking for decent potential Stocker bodies. So, some of these guys will probably either have something or know where something is that will work.
Checking for '77 GP's 1st. Not gonna list any that $10k cash or less won't buy.
https://www.autozin.com/for-sale/pon...#carid=2731211
https://www.autozin.com/for-sale/pon...carid=14425317
https://www.autozin.com/for-sale/pon...#carid=2841908
https://classics.autotrader.com/clas...prix/101513093
https://www.autozin.com/for-sale/pon...carid=14444230
https://classics.autotrader.com/clas...prix/101427485
Wow ! To my surprise, there seem to be more cheap '77 Birds than GP's. Don't know if any of these are decent enuff to use to build a Stocker, or not. But, there are some for less than $5k. A couple of years back, I bought an '80 Bird, with a '77-'78 style nose, for around $3500 shipped. So, hey, a '77 Bird with a 350 Pontiac engine might be one of the cheapest '77's to build. Lotta rust bucket Birds out there, tho.
https://www.autozin.com/1977-pontiac...289-atzlisting
https://www.autozin.com/for-sale/pon...#carid=1801688
https://www.autozin.com/1977-pontiac...855-atzlisting
For those who can spend $10k for a body, this '78 might work. I think maybe you can change grills & claim a '77 model.
https://www.ebay.com/itm/13386311715...=&toolid=10050
How 'bout a '77 Bonny ?
https://www.autozin.com/for-sale/pon...carid=14381941
Don Turk had his GA for sale, for quite a while, for $10,500. That was a bargain. I'da bought it myself, if I'da had the money.