Home gardening
Saltwater fish keeping (can be done on the cheap)
Going to yard sales looking for treasures then selling said treasures on eBay
Scale modeling
Coin shooting
Hiking
Fly tying
Agreed. Maintaining an aquarium on the cheap (IMO) is better for the fish and more rewarding as a hobby. What I mean by that, is that once you understand the basics about the fish themselves and the water chemistry that they live in, you'll soon realize that you don't need 99% of the crap marketed towards maintaining fish. Most people pump their aquariums so full of expensive chemicals that don't really do anything that it's amazing there's any water left for the fish to swim in!