Fish tanks are great hobbies! Are you going to have just fish or live plants as well? Keep your eye out for Petcos $1/gallon sales - you can get 40 gallon tanks for $40, 55s for $55... I would recommend picking up lights/filters from garage sales (hell tanks too if they are in good shape). I got my heater, air pump, 2 hang on back filters, and a spare 20 gallon tank at a garage sale for $10 - and this is pretty common.
Here is my 40 gallon breeder that I put together this summer - with fish, plants, tank, filter, heater... I spent less than $100. The hood and lights however are DIY as well as the CO2. I would highly recommend joining a tank forum like plantedtank.net - great source for info but also for cheap plants, people are often giving their cuttings away free as long as you pay the shipping.
[video=youtube;nIysWfTOT_A]http://www.youtube.com/watch?v=nIysWfTOT_A[/video]
My tanks summer progression:
I'm all about doing it the easy natural way so I started with a soil bottom tank - the soil provides all the plants with nutrients so that the tank never needs dosing. The soil and plants also help filter the water and provide oxygen so I rarely rarely ever have to change the water and I don't have to use any air stones/air pumps.
Cycling is important but you can start the process by purchasing a few cheap hardy fish like neon tetras or cloud mountain minnows. If you preplant your tank before adding fish the plants will actually cycle the tank for you.
Good luck! It's a great exciting project.