I think the best way I've ever heard it described, is that a banshee isn't a ride, it's an experience. They are pretty tame if you just putt them around, but once you hit the powerband, you better hold onto your ass. I let a friend ride mine around on the street a while back. When he first rode it he took it pretty easy and wasn't too terribly impressed. I finally got him to really get into, and get into the powerband. By the time he hit third gear he was already trying to figure out how he was going to talk his wife into letting him buy one.
A banshee can be made to be a decent trail bike, but there are much better bikes out there for that. When it comes to the sand though, you will not find a better bike.
As far as the cost goes, if you can resist the temptation to buy a bunch of goodies for it, it really isn't that bad. Chances are though, that it won't happen. Bone stock banshees are kinda like bigfoot and the loch ness monster. There are some people that really do believe they exist, but nobody has really ever seen them.