Ich is a parasite, but it usually shows up when fish have been stressed or are not really healthy (ie: have been injured). I have had enough fish with Ich to know that it's not as "easy" as they claim to cure. Typically what happens is that ich is not the only problem. An injured fish will have ich on the outside and an infection somewhere, or the ich itself will cause an infection which requires antibiotics.
Feeder fish cost $.29 each- a bottle of Coppersafe to treat Ich cost $4.00. I think you did the right thing 
If you want to have fish around for long, get a tank with a filter, start out by dechlorinating and adding coppersafe, along with a bit of salt (the type they sell in the fish store for salt water fish). Add a couple regular goldfish (will cost about $1.50 each). Beware, though, the first couple fish will probably die while the tank is building up it's bio filter. The tank while go through an ammonia spike (unless you ph balance it) which will burn the fish. If you ever see a fish in the store that has odd looking black on it, it's been ammonia burned). Once the bio filter is working, you never want to make drastic changes. Don't change all the water, don't change all the filters and don't add or subtract too many fish.
And, goldfish can get constipated (especially big ones). We had one that was about 6 inches ling get constipated. Unfortunately, we didn't know what was happening until it died. A few weeks later, we noticed that the fish store had a skewer with zucchini, romain lettuce and peas floating in the tank. I asked what was up with that, and they said that the fish were getting constipated, so the veggies would help them. Who knew?
I guess what I'm saying is- don't get fish
