I think $650 is a fair price. I bought a mint-condition DC-3 for $650 using "Buy it now." But, I also had to pop for another $100 to retube it, since the previous owner replaced the 12AX7s with 12AT7s (which sounded way lame). Although DC-series amps sometimes sell for as low as $500, these amps are so cool, IMO, that anything under $700 is pretty much a good deal in my eyes.
Note that the DC-series amps tend to be fairly "dark" (at least mine is). Don't expect the presence, treble, and punch of a Mark IV out of a DC amp. DC amps tend to sound very mid-rangey. To be honest, my DC-3 doesn't have quite enough treble to be my only amp (it does get markedly better as you turn it up though), but A/B/Y this amp with your "bright-sounding" Stilleto, and you'll be in heaven. I have my DC-3 A/B/Y'd into my Mark IV, and it's the best combination of sounds I've ever heard. Having the GEQ of both, DC-series and Mark-series amps dramatically broadens your tonal pallete, and once you've had it, you'll never want to play an amp without one again.
