well first off, P18s you can find new for like 250 to 300 tops, so used ones are not worth that (as soon as they're mounted, they are considered used). secondly the skis are around 600 new, but now is the end of the season, so they go for around like 400 a pair, and that's new, so you would also have to drop the price of those too since they have been mounted and used. the typical system used here is like the TGR one, which is for the approx max price you should get:
50% of current selling price (not MSRP)
-10% per year old
-10% per times drilled, per core shot, per delam...etc
-10% per marker binding attatched
+10-30% for Rare/High-demand item
so thats 150 for bindings and approx 250 for skis considering 500 is a greedy asking price now for stores, so you should get around 400 for the skis and bindings, but asking reserve for the price you expect is pretty unreasonable as most people on this site are broke (i know i am), making 300 pretty fair with anything more made as an added bonus.