I have to agree with Ed Buckley's recommendation of Trillian. I've been fooled more than once by it's contrabass as well as electric bass accompaniments by online friends posting songs.
Pretty pricey, but in this case, I think you get what you pay for. Last couple of years, I've been playing my own bass parts and getting closer to the end goal of something I can be proud of.
You can get into a pretty nice electric bass sound with real hardware for about $250 total: $120 for the bass from
www.rondomusic.net and another $100 to buy a bass amp simulator.