The Audio Buddy doesn't do what a Sansamp does. It might work as a DI, but you're going to be limited to one tone, and it probably won't be all that fantastic.
The SansAmp Bass DI is pretty fantastic, although very very subtle. Also, it really doesn't put out much juice, so it's recommended that you run it through a preamp prior to hitting your machine. I run mine through an ART Tube MP, which I also use to power it (the bass di takes phantom power which is nice).
Speaking of preamps, the ART Tube MP sounds really good for running bass direct. You're not quite as limited in tone as you are with the Audio Buddy, but you still don't have a whole heck of a lot of choices with it. Either the sound works or it doesn't. If you can't afford the Bass Driver, then I would recommend the ART over the Audio Buddy for bass guitar. It's got enough sympathetic dirt to work well, where a more sterile preamp might not have much life. (is that redundant?)
Really it does sort of boil down to what you like though...so it's best to try these things out. Unfortunately that's not always possible.
Slackmaster 2000