You said you were on a budget, but I'm still going to suggest the Darkglass X7 (or X Ultra).
I've spent (wasted) more money than I care to admit on the "perfect" dirt pedal for metal, and was never satisfied until I got the Darkglass B3K. About five years later the X7 came out. I told myself I didn't need it but GAS got the better of me, and I have zero regrets.
The thing about bass distortion is it very easily gets buried by the guitars. The best way to get around this is to process your clean signal and dirt signal separately. You'll want clean and compressed lows and distorted mids and highs, for example:
Bass>compressor with slow attack/fast release>distortion or preamp with blend knob (B3K/B7K)
Or
Bass>blender (eg.Boss LS-2)>distortion in one loop, compressor in another, blend together for clean lows/distorted highs
I prefer the Darkglass X7 because it does all that in one box, but it is fairly pricey. But take my word for it, it is worth it. I have happily sold all my other dirt pedals (except for a fuzz and the B3K for sentimental reasons).
Whatever you end up buying, make sure it at least has a clean blend, make sure your amp and cab can produce the sound levels you want without farting out, eq your signal so it fits with the rest of the band (don't boost bass too much, cut a bit at 400-500Hz, boost at 800Hz to 1kHz) and make sure you're using new strings! Preferably stainless steel roundwounds. The best gear in the world will sound like crud if you're using dead strings.
Good luck!