I bought most of my US games before prices went completely nuts (though still spending $100+ on those that've been pricey for 10+ years), not buying more than a dozen or so over the last several years combined. Instead, I've been buying PCE games; they've also gone up in price, of course, but there's still tons of 'em that're original MSRP or less. Not including PC-FX, PSP, or Vita stuff, I've probably averaged somewhere around 25 games and $400 worth bought in each of the last three or four years, with the average price per game skewed higher by one or two pricier titles each year; roughly two thirds come from ebay, and the rest come from pcefx peeps.
With prices the way they are now, I wouldn't advise anyone to start in with US collecting, not unless they're willing to stick to buying only the relatively cheap titles (many are still original MSRP or less), leaving the pricey ones for PCE versions, CDRs, and flash carts.