If it's just a solid piece of plastic with no logo, I don't know if I'd even bother buying them ... I'd consider it if they were really cheap (50 cents or less) since I have that running-into-furniture problem.
If they have a nice logo (either Muppets or Palisades), I'd pay $1 each.
In terms of shipping, I think it should only be $1-2 for up to 10 bases shipped in the U.S.
I'm basing this on the following assumptions:
U.S. shipping would be very cheap, since they barely weigh anything. Creating the bases would cost almost nothing; you could use the existing molds and relatively low-quality plastic. Stamping a logo would cost a little, but not much. The prices I mentioned would cover your costs, plus a little extra. Obviously, you can't expect to make a lot of profit off bases ... it's more of an increasing-fan-goodwill thing.
As I said, those are assumptions. I don't really know what would go into making them. Of course, Ken, if you can explain the reasoning behind why they should cost more than this, I'm willing to listen.
Then again, if you just sent them out as a free bonus to Collectors Club members ... that'd be nice too.
Wow, that was way too long of a post for flat little plastic bases.