The Series 24 is basically the same desk as a Series 65...just a 24 buss rather then 8 or 16.
Personally...I disagree with Rick to a point. I dig the rock & roll tone & they're pretty logical, workhorse desks. You could do better if 'ya can spend more...you could also find MUCH worse out there.
I could see a 24x24 going for about $6K on the low end...maybe $7500 or $8000 on the high end. Does it include patchbays, cabling, any spares? What sort of condition is it in? Bum channels & dead EQ's/micpres etc. will obviously detract from the value...having spare channel strips & parts, cabling & bays will add...
I owned a 28 channel series 24.
Sold it around 1997 for $11k included stand, power supply, pro co TT molex patch bay, JL Cooper MIDI automation, extra bulbs, knobs and an extra channel.
Work horse nails it for me and it did have it's own little sound. While It didn't have the balls of a Neve or definition of an SSL it served me well and I made many records with it. I don't have a clue what one would go for these days.