In this sort of thing, the KISS principle is best. If we know only 30 people want them, then $30 a pop is fine and we sell 'em out right now. However, if the assumption is that we a) have more than 30 people interested, and b) we want to raise as much money as possible, then allowing multiple chances is the way to go.
The reasons I'm suggesting a $10 minimum are:
1) we need to cover postage
2) we need to cover Paypal fees
3) we need to be certain that we don't lose money to those who only donate the bare minimum.
4) lowering the minimum donation increases the number of chances and correspondingly lowers both the odds of winning and the actual amount of donations (in a limited number of donors) IME.
If we had something of greater monetary value, I think a lower price would generate more income, Bo, but for a CD, I think the entry needs to at least cover costs. I'm not sure $5 would do that.