I would get a decent quality 100W heater. Set it to 80F and it should have no problems keeping your tank up to temp. Heaters are one item you should not skimp on when it comes to equipment as more often than not you truly do get what you pay for.
My heaters have no problem maintaning a temp close to 80F in the winter. I keep the heat in the house at a cool 68F so that means the heaters have to bump up the water temp to 12F above abient. The higher you have to get your tank temp above ambient the larger the heater you need. I have a 100W in a 20 gal
and a 150W in a 45 gal
and a pair of 250W in my 80 gal