Reducing current made by a filter?

I recently put a male rose tail Betta in a 5 gallon tank with a large mystery snail. It's heated to 80 degrees, is moderately planted, and has a filter. The current the filter makes in the tank is too strong for my Betta and his fancy fins. He's being blown around all over the place.

Any ideas on what to do to lessen the current? I've already tried strategically placing plants and decorations in his aquarium. Should I just invest in a sponge filter or is there another (cheaper?) alternative?