Honestly if the frog is healthy it will outgrow that so fast that if you're tight the best thing would be is to get a large plastic rub, usually about £20 so i would imagine $20 something, if you're needing heat at any point a 5 gallon is not great as it is difficult to heat in a way that provides a good thermal gradient IMO but if you're temps are at 80oF you won't need a heater until it drops below 78oF