We swap bottles for Airgas at work.200 cf oxygen bottle $24.00 Ac4 $48.00.The smaller OX 125 costs more than the OX200,bout $28.00 and the AC3 bottles are $42.00.There is no way an exchange on the bottles you have should cost that much.
Most Airgas dealers will swap bottles if you have a bill of sale and the bottles look to be current(good paint/caps etc.)
Same as mentioned before on the Victor regs.There isn't much to rebuilding them,you just won't be able to get the parts.Same thing here,about $60-65 per reg for a rebuild.On the other hand if they are working and not leaking don't worry about them.
There usually is tons of torch stuff on Ebay and it usually sells fairly cheap.NOS stuff doesn't even bring much,it should be possible to get a set of NOS two-stage regulators for less than $150.Don't just stick to Victor,Purox and Smith make some nice stuff too.
I just need one more tool,just one!