Yeah, the Nintendo
Dev. Kit is expensive (to say the least.) But, there are non-licensed kits that contain re-writable test cartridges, there are emulators to test code on the computer and there are compilers for both assembly and c freely available on the internet. In fact, the cartridge-writing kit (about $200 US) isn't really necessary (although it helps significantly in getting animation timing done), bringing the cost down to time.
If it turns out that the idea itself is enough to sell the game (it won't be) and a company decides to fund the project, then a Nintendo kit is probably the better choice. But a couple hundred dollars and plenty of time is all that it really takes*.
Eat chips and pretend they're fried potatoes,
* as long as your team is located in a country w/ no laws requiring that workers recieve payment