Cheap dosing pump = loud dosing pump! If you dont mind that or your tank is someplace noise is not a factor than o.k.
Just get a cheap used medical dosing pump with the drip detector and alarms disabled, and forget about your controller. Used medical dosing pumps can be found on e-bay for as little as $25-50 bucks. Or Reef dosing pump/innovative aquatics has "refurbished" used medical with the drip detector,alarms disabled for as little as $100-150 and up. HIGHLY Recommended.
Definately the way to go, unless you want to go the reactor route!
Later..............Herbie