Use an A/C, then you are nice and comfortable and your tank doesn't averheat. It'll cost you the same in hydro and purchase price.

chiller
 

my first inclination was to say yes, cause with only 50 gallons, temperature changes very quickly in relation to the ambient temperature. However, I did vote no because if it gets too hot, your tank is small enough to cool down quite quickly. Fans work great, but you have to deal with the evaporation.
Cheapest solution is for the super hot days, throw a 4 liter milk jug full of frozen water into the sump, and it will work great.( that's what I used to do cause it only gets super hot a few days here in Vancouver) Now my tank (120 with 50gal sump) is controlled by aqualogic drop in chiller. I maintain a constant 79 degrees all year round, but at a cost of $1400 was it worth it?
It was to me, but I'm just lazy and don't have a lot of time for maintenance.