Here's what I can offer...
Without intending to offend, indiefolk, I think you should reevaluate what a good guitar tone is. As pointed out earlier, a guitar is not a bass-range instrument, and by making it one you'll be walking all over the bass and kick drum. It is a mid-range instrument.
If your midrange sounds like crap to you, you probably just haven't played through a great amp. Also, as mentioned before, the scooped metal sound isn't really bassy, it just sounds that way becasue all the mids are sucked out. Then again, what the heck was EVH thinking when he put a humbucking pickup in a Strat?!
$600 is a tough price point because most good tube amps are more than that, and most transistor amps come in around $350 or $400. I would say used is the way to go. Look for a great deal on a Boogie/ rectifier type amp. If you want something new, I would look into the Marshall Valvestates. Although I don't particularly care for them, they are probably the closest to what you're after in your price range.
I have never heard a Peavey transistor amp that I though was worth a plug nickel, Bandits included.
My best advice, wait and save. Buy the right thing the first time. Anything else is wasting money.
And lastly, the notions that all amps sound the same once they're recorded, and that all amps are good becuase really smart guys spent a lot of time developing them, are absolutely crazy!
Aaron
http://www.aaroncheney.com