Your missunderstanding I think, this isnt a bolt in deal where you can just buy certain parts, The Y pipe most likely will have to be custom fabbed at the exhaust shop along with thte rest of your exhaust.
And if you cant afford headers, you cant afford to do the swap. Your going to have the $20 here, $20 there thing come up with parts you need, plus the cost of the major parts.
okay time for the answer. you can use stcok 88-92 f-body manifolds and they clear quite well, you can use lt1 style manifolds and do some fender and frame whacking to make them fit, you can also use fullsized truck 350 manifolds from 88-98 with ALOT of fender, frame and firewall hacking. the y-pipe will be custom bent at your local exhaust shop and it will cost you anywhere from $100-$300 depending on the shop. most places can and will hook it right up to your existing exhaust to keep costs down, but a full system is best. here is a pic of the 88-92 f-body manifolds with factory smog tubes still attatched. they are pretty plentiful in the wrecking yards.
if you are running a built engine, those manifolds will be a major restriction in power. but they work and are cheap. if you run a 4x4, the y-pipe is an ass pain to fab up. it took the place i had mine bent at 3 hours to get it right.