don't expect nummbers. the game of guessing what's the least amount to donate to become contributor is not well liked around here. the textbook answer would be give as much as the software is worth for you. but thats quite vage i think. as a rule of thumb i would suggest you donate about as much as you would pay in a store for application that is:
- not or sale
- not super expensive
, but costs enough so you would figure it's a worthy and useful prodct.