Get a 2.5 gallon tank, a HOB(hang on back) or Sponge filter, and use the fleshless cycle process
Directions can be found here
http://www.ultimatebettas.com/index.php?showtopic=8199
You could also do 25% water changes 2 times weekly or 100% water changes once weekly, most fish wouldn't be able to handle the stress of 100% water changes, but bettas are pretty hearty and when I didn't have filters for my 2.5 and 5 gallons, they did fine with 100% water changes with no ill affects
Be sure to buy a 25 WAT adjustable heater and thermometer too, keep the tank at around 78*-82* and don't forget to vary your bettas diet. oh and water conditioner is a must, I usually don't ad that but i forget some people just don't think about it..
also, don't forget a lid, bettas are jumpers.
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"Unlike other fish, you can add the betta directly to the water without acclimating him (putting the bag/container in the water to equal out the temps)"
That is false. Bettas need to be acclimated just like any other fish, yes, they are hearty, but not indestructible. they require the same care as any other fish.