Skins are already in development for vBulletinStyles.com, I am just awaiting their delivery. The actual design for vBulletinStyles has been completed and there is little coding left to be done so I am looking to open up shop as soon as possible, pending I get the styles as soon as I am looking to get them.
As for the pricing, they will vary from $20-$50, most being in the lower area unless designed in a more technical style than others.
Regarding free skins, phpBB is a free, open source bulletin board and many push out skins for it. Skins do take time and decent ones that are not just thrown together are going to cost a little. You remember the saying "there is no such thing as a free lunch"? Well that basically applies to everything, nothing in this world is free, at some point you will have to pay.
Chances are you don't have to pay for phpBB, but you do have to pay for the hosting. If you are not paying for the hosting, chances are the uptime is not the best (if you are on one of those free hosts like lycos).
It all comes down to how bad you want something as to whether or not you think it is worth paying for it. You obviously though vBulletin was a good investment, skins cost a fraction of the cost of vB

.