Which marketplace are you getting those fees from? I'm looking at Coinbase and its fees are quite a lot higher than that for using a Credit Card, and bank transfers cost a lot more.
However, I just tried setting up a new transaction and the fee looks to be $0.99 for a $5 investment. At ~20%, this sort of averaging would no longer be worth it. Like I said before, I guess I've been grandfathered in after the new fees schedule was imposed. Let's see how long it lasts.