I've always wanted the Busman ribbon to play with, and maybe it's the right tool for the job. But, as others have mentioned, ribbon mics put out a very weak signal, so you need a really good preamp with a lot of gain, or you will get a lot of hiss in the background. My gut feeling is that the Tascam interface isn't the ideal device for that. USB Bus powered preamps are not generally thought of as quiet preamps. Also, ribbon mics are generally thought of as much more delicate than condensers... the slightest breeze would break the ribbon. I'm not sure how careful you need to be, but that's what has scared me away from ribbons.
Consider the ADK A-51. It's a basic large diaphragm condenser with fixed card pattern. There have been several "series" of the A-51 over the last few years, and I'm not able to tell you if one is better than the others (mine happen to be series 6). Sometimes in the past they go for as little as $75 each on ebay, when they have a bunch of "last year's model" to get rid of. Without a special deal like that you should be able to get a new pair for $400, or a used pair for $250'ish. I've never used it on cello, but it's a pretty decent mic in general, and strings in particular, so I thought it might be good on cello.
http://adkmic.com/catalog/audiophileseries/A-51.phpThe OP mentioned the Crown GLM100... that looks kind of like a "pickup" that you would clip to the instrument, but instead of PZM it's a condenser mic. Our responses have all been about mics that would sit on a stand some distance (a foot or two?) from the cello. Big difference in what you'll get for sound, and I think most people are thinking that having a larger mic some distance from the body of the instrument will get you more ambiance, but that only works if you are in the right room.