I checked around, and they are hella expensive. The starting price for one used is almost always right at $100.
We used to have one long ago, but I'm fairly sure my grandma threw it in the trash or gave it away to someone. I haven't seen it in ages.
If you're looking for something just to play NES games on I'd suggest this SNES/NES FC Twin console.
I picked one up for when I was streaming video games, and it's a great console.