I would try and figure out what your potential is for selling tickets and compare it to how much you would like to make... If you have 10 people who will be helping you sell tickets, they should be able to sell 10 tickets each. that is 100 tickets. So if you want to make $500 then you would have to have the tickets be $5 each.
Start there
How many people will help you sell tickets?
How much money do you want to make?
Because you are just selling chances it does not matter how many chances you get it matters how much money you make, so if you want $5 from each person do the one chance for $3 or 2 for $5 most people will pick the 2 for $5, and tell your ticket sellers to push the 2 for $5.