I think the price is very locale dependent. Around here, New Vaqueros in brand new condition are going for around $ 850-900, before tax etc. First gen Vaqueros are quite rare around here and usually pretty used when they do turn up.
For a pristine first gen Vaquero, blued, as you describe, I would consider $750 or less worth looking at and $600 and under, a steal! I've been following GB prices and sold used has occasionally dropped into the 600s the last few months, but then one doesn't really know the condition and those prices don't include shipping which has really gone up, GB fees, taxes, transfer fees, etc.
(BTW, saw a used but pristine Ruger Blackhawk, blued, 4 5/8 inch barrel, in 41 mag (a rare one around here!) at a LGS today for an amazing $579 if I recall right; would have claimed it if my 'mad money piggy bank' hadn't been empty!)