Yeah, the Apex Gold system is crazy expensive, but it comes with a lot of stuff. The one I have (Apex Jr.) costs around $220, but it just comes with the temp probe. If you want to control pH, you have to buy the ORP module ($100) and the pH probe ($30). So the total cost for my system is at about $350 right now. In my opinion, if you're gonna get a reef controller for a freshwater tank, don't go much beyond entry level - and that's what I did (though I am looking into more modules so I can use it to dim lights).
Although it isn't necessary, it adds peace of mind that I can check on the tank and see what's going on at any time of day. It is also a safeguard in case the heater decides to try to cook my fish.