The semi-auto Thompsons are wholesale priced at around $800.00 US (I have no idea what the dealer mark-up is on them, but I'd guess at least half again as much...).
On the other hand, a Romanian semi-auto AK-47, double-stack magazine (one 5-round, one 40-round detachable) in 7.62 X 39R caliber can be had for $259.00 US wholesale; this includes enough US made parts to satisfy ATF requirements, including the firing mechanism.