Depends on where it is and what condition the running flathead is. Seems like in Texas they go for 3 easy payments of $19.95.
im so glad the fad is dying out with all the ratrod guys, the prices started to get rediculas. now the prices are starting to get decent again.
In general, assuming the running flathead is sound with no major issues my estimate is between $350 and $1,000 mostly depending on what is in and on the motor. If it has a stromberg, a nice cam, alum. heads, mallory, etc.. A lot of guys will want to buy a running flathead to build up. When you tear them down there are often problems to deal with, you never know till it is tanked, fluxed, sonic tested or whatever length a person wants to go to to make sure the block is sound. If this is your intention you may be better off looking for a sound, tested, block and build from that. Good luck, running a flathead does not have to be a big expensive deal, unless you have to hire everything out and if that is the case you might as well give up and go for a 350 like so many others do.