One suggestion, unless you already have a 10 gallon tank. Wal-Mart has a 10 gallon tank set-up for 27.00. It comes with the tank, lid, filter, net, and trial size food packets. It's an exceptional deal for that price. They have 5 gallon set up's as well. With that, you would only need to grab a heater and the other items you want to decorate the tank with. Which you could get over time.
Also check Craigslist, people sell tanks with all the items for set up super cheap when they decide to not have fish any longer. It might take awhile to find what you want but would ultimately save you money. We have gotten our 2 big tanks off of craigslist for more than half the price of what they would have been in the store.