If you have a petsmart, they have the top fin 5.5 gallon starter kit for $28. All you need to add to it is a heater and a thermometer. I have the 29 gallon version of this tank and am pretty happy with it. If you have space, the Grreat Choice 10 gallon starter kit for $30 is pretty nice. Just add heater. I have the 10 gallon and am pretty pleased with it. If space is a premium, the Top Fin Aquascene 3.5 gallon is on sale for $23. An heater ran me $10-$15, so if you need to stay around $30, that's your bet.
BUT, and here is the best part, if you get the 10, you can always make a divider and get a second betta. And since you already have the filter, heater, food, water conditioner, and space, all he costs is the price of himself and a divider. And trust me, bettas are like potato chips. It's really hard to stop after one (i currently have 5!)