These propellers are flexible and won't easily break or cause damage to motor bearings upon impact. They are very affordable and are available in a number of sizes. (3x2 - 9x5) Go to page two for larger sizes up to 12x8.
Propeller sizes 3x2 through 5x4.3 have 4mm holes in their hubs.
Propeller sizes 6x3 through 12x8 hole the old school 3mm diameter hole in the hub. The hole size can be reamed up to 6mm to accommodate your motors shaft.