How much is the proper amount to give for Matanos L'Evyonim?
Mishnah Berurah 694:1 cites Ritva that the minimum is two perutos.
He also goes on (ibid. :3) to quote Rambam, that it's better to spend more for matanos la'evyonim than for the seudah and mishloach manos. Considering what lots of Purim baskets go for nowadays, that suggests that the proper amount for matanos la'evyonim is quite a bit more than two perutos...
The Gemorah states that one must give one gift to two poor people. However, the Gemorah does specify the amount of these gifts. There is a dispute among the poskim as to the exact amount of money that must be given in order to fulfill this mitzvah. Some state that it should be an amount sufficient to enable the poor person to purchase bread weighing the equivalent of three eggs (Zairai Emes Vol. 1-11, ST 694-1). Some state that even a small coin (nickel or dime) is sufficient (Ritvah Megillah Daf 7a). Others state the amount needed is the amount equivalent to the cost of a meal (Pri Migadim 694-1, MB-2, Rabbi Moshe Feinstein Zt"l, etc.). Therefore, the amount should be around four dollars (American) per poor person.
The Ben Ish Chai (Shana Rishona, Tetzaveh Hilchos Purim paragraph 15) also says that Matanot La'evyonim could be food (at least 3 eggs), but if you're giving money it should be enough to buy "bread weighing the equivalent of three eggs".