I'd say you did pretty well. I actually paid about $200 for my Twin Famicom, 5 cartridge games and an FDS disk, and I don't regret that purchase at all. I've always been kinda paranoid around using the FDS, but since it seems to be getting easier to find supplies and info about fixing it, maybe I should need not worry.
You probably already know this, but the AN-505 was the 2nd Twin Famicom model released, and it featured rapid fire buttons on the controllers, therefore making it command a little bit more money than the first model AN-500's. I've got a red case/black highlight AN-500, and I think it looks mighty slick. I've always loved the case design of the Twin Famicom for whatever reason.
One question: Was the console domestic or foreign? That is to say, was the seller in the US or did you pay for overseas shipping? When I bought mine, I bought it from a seller in Japan and it ended up costing a good deal for EMS shipping. But if you bought yours for $100, that's certainly nothing to sneeze at, especially for the reasons mentioned above.
"You made...a great deal!"