I remeber seeing a number of people selling stock cast 440/400 pistons on ebay for cheap. Been some time since I searched, but they were like $18-$20 each.

I looked into building a 400 block/440 cast crank stroker with oem cast 440 pistons. Wont achieve 500 cubes, but its probably the lowest $ stroker you could build. With cheap ebay pistons, and stock crank and rods, the biggest costs would be piston reworking (valve reliefs and cam clearance) and your general machine work and balancing.

Read here: http://www3.sympatico.ca/big-d/460.htm

I ended up with some 440s so I went that direction instead.