Tires for use during build

[freak]

After doing nothing for a while... I need to get my cab back on my frame to start adjusting the floor, doors, rockers, etc. Problem is that my tires are mismatched and leaking. I would like to get a set of used 235-75R15's or something close but nothing is to be found. I called the local shops and one guy said used 15's are like gold. Said 15's don't come on anything so they're super rare these days. Others shops said the same. Craigslist has nothing but sets that are expensive as well. I'm not going to alter the suspension from stock but I'm not sure what size tire/rim I will run when done. I also don't really want to buy the final and probably expensive tires to use during body work, welding, painting. Also I could change my mind by the time I get the frame and bodywork done. The cheapest thing I can find is about $70 x 4 at walmart. That's a lot of money for tires I will probably never use. Should I do it anyways and try to recover the cost by selling them later or is there a better option that I haven't thought of?