I use my Tech 21 SABDDI for exactly what you are asking about. The SABDDI has some base settings and one of them is an SVT setting. It's not exactly an SVT but some messing around with the controls and you get a very close rendition of the SVT sound. It's a great device.
I tried the Bass Attack and the others and went with the SABDDI. If you can find a place that has them go try them yourself. You can find the Sanamp and the M80 at a Guitar Center.
I tried the Bass Attack after buying the the SABDDI. I couldn't find one at a store. Nobody carried them a few months ago. I finaly found one at a small store thaty carries nothing but Hartke, Peavy and some off brand stuff. I seemed to work pretty well. I got some good tones out of it and I could have got it for about $50.00 less than I paid for my Tech 21 unit. I still think the Tech 21 is a better unit and don't regret buying it at all, but if you are on a budget the Bass Attack will get you by.
Thanks for the advice SRX, I think I'm going to go with the Hartke (thanks to an awesome deal from mike) and maybe try the mxr and tech21 if I can find them in a store. I'm nowhere near a GC so the chances of finding bass effects locally are pretty slim.