As the Official Terb Spokesman for Under Armour (check Under Armour thread); Under Armour is awesome but I don't think it is cheaper than the Nike dri-fit.
The Nike Sphere shirts (Nike next gen Dri-fit) are great and they soak up the sweat quite efficiently.
For the best price, just shop around. All the sports retail stores sell some time of Dri-fit clothing and there should be some great sales on outgoing stock. Nike, New Balance, Reebook, etc.... all make dri-fit so you should have no problems finding a wide range of selection.
Even Running Room sells their own brand of Dri-fit so you can even check with them.