He's very cute. :) Normally for a one gallon container, I recommend 100% water changes every other day, but if you test your tank regularly and things seem to be working out with this routine, you could stick to it. If you add a hardy live plant like java moss, you'll get a bit more wiggle room as well. Plants absorb some of the wastes fish excrete as food and just a bit of moss can make a big difference. You should look into it. :)
If you want a cheap temporary home for your betta, you could use a rubbermaid/sterilite plastic storage bin. They're not the prettiest containers in the world, but the clear ones are only about $3 for a 4 gallon bin--you can't beat that. Plus they're safe to use with a quality adjustable heater, which your boy needs. :) They're very durable and light for easy cleaning and make great betta homes. If you want to upgrade to a setup like this, I recommend this heater or one like it: http://www.fosterandsmithaquatics.co...8&pcatid=11368
since it has an adjustable temperature dial, you have more control and stability. Nonadjustable heaters often don't heat the water enough or overheat it, so you should avoid those.
Good luck and welcome to the forum.