Under $4k budget build LA360 build

Bummer. Has the block already been bored .040 over? if so, then the choice of pistons will depend on whether you want the lightest piston available (hypereutectic) or the strongest (forged) along with cam/compression compatibility and profile (domed, flat top, cut for valve reliefs, etc). Just me again, but I wouldn't be shopping around for used piston no matter the condition; when I chose mine I did so by availability and cost and did a side-by-side comparison, as by choosing I boxed myself in to a set of .030 pistons and had to have my std block re-bored.