Frogs as Pets - Pros and Cons and Good Species for Beginners
This should answer most of your questions. In general 1-2 frogs can live happily in a 10 gallon as long as they aren't too big or incredibly active. Feeding shouldn't cost very much considering that crickets and mealworms are only a few cents each. You could also breed insects for an even cheaper food source. Just reply to this if you have anymore questions!