Sorry to get involved...But peaches, on bettatalk the 1/2 gallon thing is like her last choice and she even says to clean it every 3-4 days. She doesn't even recommend it. And she also says that bettas in that home style are more likely to get fin and tail rot and other bacterial diseases.
When she's talking about recomending the 1/2G she's refering to people that have alot of bettas, mainly like breeders, which is EXTREMELY expensive to keep them all in tanks. Plus, there all gonna be sold to people with bigger homes. the 1\2G is just their temporary home.
Not saying your betta's gonna like die right away or anything, but your heading to many problems such as tail/fin rot and other bacterial infections which in the long run will be more expensive. PLUS by getting a 2.5-5G tank your just making your life easier, and expanding your fish's life longer.