If you particularly like the amp(s) you have now, look into the method described by moltenmetalburn for the cheapest results.
Alternatively, you can get an attenuator with a line out and use it as a dummy load. Run the line out into your DAW and use a convolution plugin for cabinet simulation and pick up some RedWires IRs. You can also get direct out box and put inline before the attenuator and use the line out of it. It will be a slightly better signal.
You can find a used Weber Mass for $150 (or cheaper if patient). A whirlwind EDB1 direct box is about $30. And let's just say two redwires cabinets for $20 (although, you'll probably add to the collection). You can always add a better line out box later.
So, for less than 200 bucks. It doesn't sound exactly like a miced cabinet, but you can get it to sound pretty decent. Pete Thorn did a comparison with his PT100 miced and direct with RedWires here....
http://www.rig-talk.com/forum/viewtopic.php?f=3&t=72321&start=50
That's with a suhr direct box though, which is about $170.
A little EQ in the DAW and I think you could get a sound you was into.
All that said, nothing really replaces a well miced cabinet.
If you don't particularly like your current amp, pick up and AxeFX or an 11R.
