I recently bought a You Dirty Rat pedal primarily for bass distortion and I love the hell out of it.
It gives a really nice dirty tone, somewhat similar to if you'd turned your amp up way too loud and your speakers are distorting.
That being said, I was surprised to find it gives a really weak distortion on guitar and the only thing it's good for is boosting my amps distortion.
But for bass it kills.
http://www.ratdistortion.com/youdirtyrat.htmas for the cost, i scored mine on the american ebay for about $100 AU
If you haven't been looking at the american ebay recently, start doing it.
The american dollar is weak and the aus dollar is trading at .95 so you can often find musical equipment on ebay for half the price it goes for here in aus.
My mate has a boss Bass Overdrive pedal and it's fairly disappointing. All the boss distortion pedals have a really thin kind of distortion, imo.