Really depends on the size of your tank and the range of the temperature swings. An adequate amount of fans for your size of a tank can probably lower the temp about 2-4 degrees. If your tank is getting up to 84-86ish when the T5's are on, you should probably just get the chiller.
Fans = slightly lower temp, more evaporation (thus causing you to need to top-off more), small energy footprint
Chiller = any temp you want, no evap, insane energy footprint