If folks would keep in mind that they are "donating" to a good cause without expectation of something in return the price of the raffle ticket does not matter.
On the other hand with the economy the way it is and with the above in mind some might not still be able to afford $5 per ticket but the fact that it also would have 3 for ten attached to it, it most likely would still pay off.
It would however leave those off that perhaps could only afford a dollar for a ticket.
Key is to figure out what would work in your demographics and economic times however do not sell yourself short by going lower than what you suggest.
Personally I would pay any price for a lottery if it's for a good cause as this one would be. I have paid ten dollars for a ticket to help high school kids get equipment and go on a trip in a neighboring town last year.
I think your thought on $5 for 1 or 3 for $10. sounds more than reasonable.