If you completely disassembled an over/under, pump, and semi-auto and put all the parts on one table, you have your answer to this question. Simply put, it costs more to build an over/under because there are so many more parts, plus you’re buying two barrels instead of one. Most over/unders have a walnut stock and fore-end too, which is more costly than composite materials often found on repeaters. Add in the scrollwork to the receiver or side plates and you’re looking at speedy shotgun.