Where I live they are usually sold for anywhere from 20 to 30 bucks a pop, and that's canadian. So if you are american it should be even cheaper.
A great place to look is at flea markets, alot of malls tend to have pretty big flea markets on sundays in which people sell mass quantities of games, systems, and so on for relatively cheap.
The only real issue you have to be aware of with the nes is the dreaded grey screen of death that most people think blowing on the cartridges fixes. That isn't the case though. The reason for this issue is the pins inside the nes in which the cart connects to, they bend too much over the years and that limits the connection that needs to be made in order to load the game.
And even though blowing on the cart seems to fix the problem, your breath actually corodes the connector chips over time. So the solution is to either buy a new connector online to install or bend the old ones back into place.
Heres a link on bending the pins, it's really not that hard but if you don't feel comfortable doing it yourself, have someone you know who may be used to handling electronics do it for you.
http://www.classicgaming.com/feature...les/nesrepair/
And yet another alternative is to buy a newer top loading nes, which loads cartridges the same way a snes or N64 does. These can be found pretty commonly on ebay but you'll pay alot for one as they are rare and in high demand. I've seen them go for upwards of 200 bucks.
Well it's a little long winded but I hope my posts helps you a little there.
