Well I won't talk you out of it, but I think based on you said about your tank and the corals in it, you'd probably be a better candidate for dosing than a reactor. Your demand will not be all that high to keep your alk and cal in check. Of course I freely admit to being biased towards dosing simply because its safer and has fewer mechanical parts to worry about. The biggest fear with a reactor is a mechanical failure at some point, like a line clogging and melting your media, co2 sticking on or shut, pumps failing that kind of thing.
Do you have a controller by chance??? If so, using a couple of Drews Pumps on the timer will be simple and cost effective.
If not, then you'd want to get a controllable dosing pump like the Litermeter. You basically calibrate it once for volume, then over the course of a week or so, figure out your daily dosing amounts. It will squirt small quantities of solution into the tank 50 or so times a day to keep your parameters stable and avoid spikes etc. The problem with them is they tend to be a bit costly unless you can get one used. New they run about $450 or so for the base unit and secondary pump.
Dosing also has a storage component to it. You'll want to buy bulk quantity ca, alk and mg. Its basically 4 5-gallon buckets at the cheaper end of the bulk quantity scale, though they do come in small quantities they just cost a tad bit more. 1 gallon of each will run you about 25 bucks and will probably last you a month or so if not longer.
So there is an initial investment on both, if you have the CO2 gear, that reduces your cost on the reactor, but a good reactor will still run you $200-400 new. The media is about the same as the bulk products...
The other thing that I like about dosing over the reactor is that you can dose in different quantities. Your tank will use ca and alk at different levels over time. So for example... 50ml of ca and 75 ml of alk per day... if you have a reactor, it basically does them both at the same level. Over the course of weeks, your numbers can flux and you end up having to dose some anyway to get it back to where you like to keep it.
Both methods work fine though, so either route you go you should be happy with the result. Its just the equipment, process and procedures etc that vary.
