Under $400 to build a frame with all new materials, minus suspension, is pretty reasonable. Since this is to be a open wheel/front roadster, a T style frame would be easy to build. Two straight rails, kick-up at rear axle. Front axle is mounted off the front cross member, no kick up required. Check Speedway Motors catalog (order one at www.speedwaymotors.com
, it's worth the $5 or so as a reference), Art Morrison, and other frame shops for pics. Pretty simple!
I have to agree that getting a good mini-truck frame to start with is a good idea if building something off that type of frame. If it's used at or near stock height (no or minimal frame mods, lower like you would the mini truck to begin with) it should be more useable. I have to agree that tryingto hack one up to make it fit isn't a good idea. But as noted, if it's to be open front that suspension will be ugly! It won't look as bad with a grille shell in front of it, but you still have those big a-arms and such hanging out there. Full model A type fenders would help hide the suspension from all but a front view. If the chassis needed hiding the body could be channeled over it if the frame isn't to wide.
I still think it's doable, but not with an open front fenderless vehicle -- not a good looking one anyway. The vehicle would have to be planned around the chassis, you can't decide to build a type of vehicle then try to make it work on that chassis. Maybe a later 30s car with "fat fenders" would work a lot better... a 36 or so.