Whatever the market will bear. There was a time when Black Paladins were stupidly popular, and a NIB blister would easily fetch $50 USD and up.
It also depends on the paintjob. There's so many 'pro - painted' models that are barely worthy of the name, it has become a joke.
Brand new, I would pay $20 USD a blister, easy. Painted, I would want to see the actual paintjob with up-close shots. If the job would score a 8+ on CMON, I may consider a higher offer.
If the paintjob were a 9+, done by a prominent artist, with all sorts of effects like OSL and freehand, and I was impressed, I would easily pay $100+ USD per unit.