I paid $900 + shipping for it last december. prices have gone up a bit since then - most seem to be priced at $1100 or more. they vary a lot, with some people asking twice that (but not necessarily getting it).
the '90s reissues are usually a little cheaper but not a ton, and most don't have the HB-1 pickups.
yeah there's a lot of variance. I think they were mostly built 1 at a time, so there's no real rules as far as colors go. not sure about the green but I've seen at least one older guild with really dark blackish green that was labeled as black but faded weirdly. I know the actual green reissues are pretty rare these days.
most have a phase switch that lets you switch the phase if you're in the middle pickup position. not sure when that started, probably 72 or 73.
if it has a weird trem, it's probably pre-72. there's a 71 on ebay right now with a weird trem. the "deluxe" models from at least 73 on had a bigsby.
s-90s have just 2 knobs, no phase switch, a larger pickguard and no binding. so they should be cheaper, but pretty similar overall. should have same pickups and everything.
They are great. Considering the price of a new USA fender/gibson, I think $1700. AU would not be unreasonable. At a shop a lil more I guess. Scarcity and all that.
I've helped fix up a couple early/mid 70s ones and they were awesome. Sold one to Stephen Malkmus and he uses it all the time.
Try to find an S-100C, with the hand-carved acorn decorations. I've tried a couple and they were both great. I think the guys at Guild cherry-picked nice S-100s to do the carving on.