At 5'6" my wife is on a small 2006 Supermoto and it fits her great with a 90mm stem. Trail riding mostly, but I'll be dragging here along to some more DH/FR destinations this summer where that bike can really shine.
Nine-hundred sounds a little steep for that discontinued frame, even if it's new old stock. Although it is a good frame and definitely worth a sub $1000 price tag...and it's likely there are no other new ones out there at this point.
For a pricing reference: We did pay almost $1000 about a year ago for her frame and at the time it was the only small SuMo that I saw around advertised anywhere. I do recall that Chad from Red Barn Cycles had bought a few of Titus's last remaining Supermoto stock and was blowing them out for around ~$800, IIRC. (Scratch that, I just checked an old email: he quoted me a price of $725 for a medium SuMo with a DHX 5.0 Coil. Damn that would've been a great deal.) That was well over a year ago and unfortunately we missed out on those...I wanted one for myself too.
I'm with Geo, give 'em a low ball offer and see what they say. If they won't budge and you still want it, go for it, it's a nice frame. I wish I had gotten one when I had the chance. But then the Mrs. and I would have matching SuMo frames and that would be a bit much.