For the inital outlay I would say they're likely about the same price. Good luck finding a used doser (although I could swear I just saw one on here, ah yes,
here it is) but used calcium reactors can be found for good prices.
For the running of the reactor versus doser its likely that the doser will cost you more in the long run depending on what kind of demands your tank has. For me, I had incredible CO2 demands (had to fill the tank every couple months at 20 bucks a fill) and never figured out whether that was just the way the reactor was or if I had some sort of issue with it. The previous reactor I had was perfectly fine. I spent probably $50 a year on CO2 (10lb tank 1.5 fills (every 9 months or so)) and $30 a year on a box of aragonite media (it got sludgy after a year so I always replaced it instead of dumping new on top). For the doser hmm, I'd say about $150 a year or so on media (possibly more depending on where you get it from).
However, when it comes right down to it, I have no problem recommending the doser over the reactor and well, this hobby ain't cheap anyways
There is no hassle of getting the co2 tank filled (remembering to do it was always a problem for me) and there's no "oh I'm out of gas" 5 days after it was actually out because you never look at the gauge so your parameters are in the toilet. For the doser, I pretty much run out of the reagents when I do my regular tank maintenance so I've worked that in, it takes no time at all to make them up (course you have to be organized enough to have it preordered so you don't run out). But for me, the best part of running a doser is that my parameters are way more stable and my corals grow like crazy. I never had growth this good when i was running a reactor. I have no idea what the deal is, perhaps its in the order things are dosed, perhaps when they're needed most or something but its pretty awesome actually having a tank of colonies instead of frags (or furthermore, having to prune back said colonies because they're getting bigger!).
Sorry for the long winded post, but I think that covers it. Go with a doser, you won't regret it. End of story
