If money is an issue, and some of us have that problem. Walmart will sell you a 10 gallon tank with no frills for $10 and then a sponge filter will be less than $10 and the airpump to run it will run another $8 or so. Then all you need to start with is a small heater and the very best heater you can get (I recommend not skimping on a cheap heater as they have to be replaced too often and the cost will eventually run much more than getting the best to start with) is about $18 for a 50 watt or 75 watt depending on which one you want. They will both work but the 75 watt will actually probably cost less in electricity to use as it will not run as much. Your little friend can get by without a seperate light for a bit if need be and later you can get a hook on or screw-on light for him for under $25 or a hood for a bit more. Gravel and decorations and plants are options and can be added as you find them and have the money. If you get the sponge filter and airpump you will need to get some airline also as it needs to be connected. You can save and not get the controllers for the airline right away by tying a knot in the airline and controlling the airflow by making the knot looser or tighter. Otherwise you can purchase a small valve that will allow you to screw a knob to control the airflow. The nice thing about sponge filters is then you do not need a seperate airstone. Be sure to place the sponge filter near your heater so the bubbling can help circulate the heat from the heater to all the areas of the tank. With 10 whole gallons the little betta will think he has gone to heaven and he will spend many days examining the space and may even just sit motionless for a bit not sure that all this is his. I will say that overall the bookshelf tank that Dave has mentioned will be cheaper and will include the filter and light. You will still need a heater but otherwise if you have the money it would be the cheaper of the options. It is just the way I suggested you do not have to have all the money at one time.
Rose
If you have not seen what the bookcase tanks look like when they are set up try this picture:
http://www.fishlore.com/fishforum/be...ta-photos.html
This young lady has her new betta in one of the bookcase tanks.