You can 100% the first three Spyro games in about 9-12 hours each. The first one can be done without any backtracking, even, since you have the same move set throughout.
I believe modern games take 100% runs way too far. I enjoyed 100%-ing the 3D Mario games… and then I got to Odyssey, and it was such a ridiculous slog that I couldn’t get much further than the standard ending.
I’m not sure the NES was affordable per se. On release, it cost about $500 in today’s money. And then you had to buy games at extra cost. In a world where you could go to an arcade with your pocket money and have a decent amount of fun, I don’t think it was a great value proposition in the eyes of many.