Such a small amount:
If it's actually a business and not just freelanced cash...
Treat your wife to dinner and talk about business for half of the meal, then it's an expense instead of being income, save $500 of your other income and invest it.
If this is stuff you do for friends...
Have them buy you dinner, concert tickets, bowling night, or whatever you like to do with them and reduce your expenses.
I do favors for friends but I don't charge them, they usually just invite us over for dinner or buy us beer and hot wings. :)