doctor v64
Not new, no. there are some used ones on eBay but they're quite expensive. There's at least one N64 flash cart that I know of that's still in production, the Neo Myth N64 cart, but even that's about $200.
Go hunting IRL. You can probably get it cheap at a flea market. Otherwise, expect to pay big bucks. Was this released in the US?
Not any cheaper:
http://64drive.retroactive.be/
this doctor v was not quite popular here in phil. but the cool thing is, it has an dvd reader..