You can pick up a used B3K pretty cheap. If it's going to be always on and you have decent EQ on your amp, you don't really need to step up to the B7K. There is also the Source Audio Aftershock which has Darkglass models in it and extensive EQ, but I found it frustrating to program and could not get it to sound as good as the real deal. Likewise something like the POD X3 Live would come up with the goods but only if you put the time in to set it up - there is a good Youtube demo around somewhere showing it set up with clean compressed lows mixed with a heavily distorted and EQ'd guitar rig and it sounded fat as hell! For hands on tweaking and baked in metal tonez, it's hard to beat the B7K.
If you want something dirt cheap (like under £24 new!) to tide you over, then the Behringer BDI-21 is a steal. It's a clone of the Sansamp BDDI, which is what a lot of metal guys use (and was everybody's go-to before the B7K came about).
Also, hang onto that ODB-3 until you've tried it going into a Darkglass or Sansamp - they both have the ability to take the fizz off the top end and make that pedal sound great!
Tons of good cheap compressors out there - read up on ovnilab.com if you haven't already. But if it's clean clinical compression you are after then the MXR Bass comp or Keeley Bassist would be a good place to start.