The ever-useful J-Station/J-Edit setup has a wealth of excellent bass amp and bass cab models as well as very sophisticated effects that work well for bass (particularly compression).  Nice S/PDIF digital out, too.
There are those who feel the J-Station is even better for bass than for guitar.  Go into J-Edit and tweak it until you have a bunch of dream settings.
Perfectly good used J-Stations can be found for under $100 and brand new ones for under $150.  At that price, lots of folks consider them a home-studio must.