Make sorbet. It can be frugal, and it's always delicious and healthy.
I make sorbet with overripe fruit I find on the discount rack at the grocery store. A watermelon with a dent in it, a pack of strawberries that are a day away from being bad. No problem!
Cut the bad parts off, blend it all up with some sugar or sweetener of choice, a tablespoon of vodka so it stays smooth, pop it in the freezer for a little while and voila, fresh fruit sorbet!
There are TONS of recipes online, and you can use any fruit or fruit combination you can think of. I love watermelon sorbet, and making a kind of frozen yogurt/fruit sherbert is easy too if you want it creamier. Just add plain or any flavored yogurt to your fruit mixture. I like vanilla yogurt and cantaloupe.