Was hoping to get some expert advice so that I can have a price range to expect to pay and don't get ripped off. The asking prices I've been getting are all over the place.
I'm leaning towards a KASHMIRI silk pile on silk base "garden" compartmental design rug. Here are the details I have on one of the rugs I"m looking at:

KASHMIR silk on silk rug, 9'x12' (275 cm x 365 cm)
traditional "garden" compartmental design
have been told that the KSPI range is 880-990 kpsi....due to the fact that the knots at the edges are usually tighter than those in the centre.
the rug uses SWISS dyes.
the silk tassels at the are dyed with several colors.

Can anyone help give me a reasonable estimate of a price range I can expect to pay?

Also, would there be any difference in price if the compartments (boxes) are smaller? For example, would a rug that is 24 compartments wide (plus borders, etc.) be worth more than one that is only 12 compartments wide, even if the rug is the same width (9')?

Thanks in advance for you advice, and please excuse my ignorance. I am just beginning to get into appreciating these beautiful works of art.

Bukhara is right, 880-990 sounds far too high. Especially for a larger rug. Might be that the knotting is Ghiordes (single) knot rather than Senneh (double knot) so it looks like there are twice as many knots than there actually is. Here's a good explanation.

I'd also watch in case it's not real silk. A true silk on silk 900KPSI in carpet in that size would cost tens of thousands.