Some Thompson cost/prices. The original relatively small number of Model 1921's were being sold in the 1920's for around $160 dealer wholesale. When the gun was finally mass produced from 1939, the M1928 that is, the first contract for 10,000 Savage was $67 each. The last lot of 400,000 M1928A1's from Savage was $59, and the company got $34 for most of the M1 and M1A1 Thompsons it produced. The cost of M3 'Grease Guns' was around $20. So the simplified mass produced Thompson's cost might not have been much greater than PPSh-41 which had wood furniture and in general wasn't as bare bones and production oriented as the M3, or Sten, or PPS-43.
But, the relevant comparison would be what US manufacturers would have bid to make the PPSh for, which we really don't know. The Soviet price even if anyone here might know it, I don't, is meaningless to compare to US weapon prices because not only the finished product but prices of all components, material, labor, capital expense of plant etc in Soviet system were determined by bureaucrats semi-arbitrarily. And, the exchange rate from US$ to Ruble was set almost completely arbitrarily.
Joe