The exact model in question here is a 6004 (2011 model), 6pt SC with switch action base clamps. The machine was used for about a year before it was sold and was (is) in excellent condition.
The base clamps he has on them now are from a 5800 (2012 model).
The machine was $700 (shipped). At the time of purchase, a new 6004 6pt SC was priced at $1349. Estimating maybe 75 to 80% value for an excellent condition 6004, that'd be about ~$1000. Take another $300 off for the swapping of 5800 base clamps in place of the original 6004's base clamps, and you're at $700.
Further considering that the $700 included shipping and shipping was about $70, I think it was very fairly priced.
Having experience with both base clamps, the switch action are definitely nicer, but IMO, it depends how many racquets you do at a time. I wouldn't want to do 5 in a row with the quick action, and I'm glad I have the switch action for those days when I am doing several in a row without stopping.
If I'm only doing a few a week, the quick action would be perfectly fine.
It's also worth noting that the quick action from Gamma as MUCH better than quick action from other brands that I've used. I used to have a Mutual Power with quick (but not switch) action, and those weren't nearly as nice as Gamma's quick action.