other than a decent 2.5 gallon tank you can get all the other suitable equipment for cheap. you can get a small whisper 1-3 gallon filter for 11 dollars. You can buy a whisper mini heater (i believe its a 10 watt) designed for 1-3 gallon tanks for 12 dollars. The only problem with the heater is it has no thermostat. It simply runs. It is supposed to raise temperature of water about 5 degrees. So if there is ever a warm day where the temp in your home exceeds mid 70s, there is a chance that the heater will bring the water temp up to the mid to high 80s... The filter is on, but almost too weak. You can step all of this up a notch to a 5 gallon tank with slightly better equipment with a price increase of probably no more than 15 dollars total.
In short. You have a nice 2.5 g or 5g betta set up for less than 40 bucks.
And your betta will appreciate it.