I agree with megaflipper about the paypal account...just see what happens. You can be like PBS and run a donation drive periodically. You could put on a tux, gussy up Liv in a ball gown and extoll the benefits of the Fierceboard. :) (At a minimum Liv needs the ball gown, you can wear shorts.) I see the benefit of paying a nominal amout $10 for something that I enjoy reading. See what floats. Myself, I like the idea of shoving a fist of wadded bills to you in a darkened hallway at the Milkhouse.
However, the sling bag idea with just Fierceboard is a good idea if you can make it profitable with the no sizes issues, keep it small enough to ship cheaply etc.
$5 and $10 donation level so that someday you don't decide to shut the board down and go coach Liv in soccer (it could happen!)
$25 donation and you get a free Fierceboard slingbag.
$50 donation and you get a free Fierceboard sling and an autographed photo of Liv suitable for framing.
$100 donation and you get to be the banner for X period?
(P.S. And you should allow a checks option in addition to pay pal for adults of a certain age who messed up setting up their pay pal account years ago and have never managed to fix it. A small category, but um, it exists!)