Price Checks

What type of mark-up is usually made (if there even is a "usual") for BPO's that range between 9 / 18 and 10 / 20? I have some ~200 BPO's from the full spectrum of sub-cap mods (including a few frigate BPO's) I'd like to sell off, the vast majority of which fall within that range. Looking at contracts for them, the prices look like they're all over the place.

I also realize that contracts tend to linger when they're bad prices, so assuming the prices I see are the acceptable prices would be a mistake.

On something like this, with so many, would it be better to just do an auction with a starting cost of 2x NPC value and a buy-out of... 3x NPC? 4x?

I've never tried selling researched BPO's before, so this is entirely new territory to me.