Low cost connector for two stacked PCBs
DW-50-14-T-S-1100 are US$3.20 at quantity 1 from Digikey. I have used them before (with fewer pins) and they do the trick.



I have also used card-edge connectors like these.  It'll probably be more pricey since you'll have to assemble the harnesses but it may still come under your price point.