Welcome to APUG
I think the biggest bang for your buck may be a Kodak 2D or maybe a Burke and James or AGFA. Some of these may be rather ugly but still work. Some may even have a lens. The biggest draw back will be less than perfect bellows, but you can get around that by draping your dark cloth over them when you make the exposere as long as they're not super ratty.
I was lucky and found a 5x7 with a shutter/lens that was ambiguesly listed on the auction site and paid $40. The bellows have pinholes but the above solution works just fine. I sent the shutter/lens out for a CLA (Flutot's Camera Repair) and bought a SatinSnow ground glass.
Don't forget to factor in the film and film holders, tripod, dark cloth, cable release, light meter, etc. If you shoot other formats you may already have some of these.
Check the auction place regularly and search odd variations of your primary search. You may luck out.
Good luck and let us know how things work out.
Alan.