Not enough info for a reasonable answer.
how rusty is the car? Do you expect them to disassemble / reassemble your car for this?
Are we talking just a get the shell fixed price? or someone restoring the whole enchilada turn key style.
Probable needs more than just a floor?
Torque boxes, cowl, rockers, ect
floor alone most likely needs engine, trans, interior, and exhaust removed
post some pics