If you got TH2 with Sonar (any of the lite versions) I think you may qualify for a discounted upgrade price for Overloud MarkII Bass which is supposedly really good.
I could be wrong on that. I got the discount for the full version of TH2 because of my Sonar purchase(s) and I can now get MarkII Bass for significantly less (haven't checked for a while but I think $100).
However you have been here for a while so you may have owned previous versions of Sonar which included GR4 which I think included the BassPro emulation. That has many of the tools you need for bass (multiple band EQ, drive and I think compression but Sonar has better compressors anyway you can add on).
I've found though if your DI bass signal is good enough you can do a lot with it using the basic Sonar tools without a sim. Cloning the DI track three times and setting up one track to bring focus on the ultra low rumble, the second for click attack and a third to add drive... then blending them together can get a pretty good sound for all sorts of stuff. This is all using the Quadcurve EQ, two stage compression and the Tube Sat/Softube Sat modules. FX Bin/Rack stuff can help it all along (like using a guit sim for your drive channel).
Getting a good bass sound from a dry signal is actually pretty easy. Getting it to sit in the mix is the hard part and there are a LOT of factors to that.
If you wanted DIY you could provide more details of what you need and I'm sure the smart fellows here could give you ideas (or try the Techniques subforum).
Cheers.