If it's the expense of a reactor, I don't blame you... however you can dial even the largest reactors down to providing the smallest of systems with Ca and Alk... Just because your system is small doesn't mean it wouldn't benefit...
Good question.... I would lean towards Kalk.... easy to do and more stable unless you drip your supplements... personally I have Kalk running straight from my auto top-off as WELL as my Ca reactor going.... and I don't really have a crammed tank.... (YET!)... Kalk is a "balanced" additive that replenishes BOTH but keep in mind that 1 dKH of Alk is only 20 ppm Calcium or something like that, so to raise your Ca by 60 ppm would mean adding 3 dKH in Alk... I've heard some people having great success ... swearing by it as a matter of fact, by using 2 part A&B supplements... even in very large systems... These are ionically balanced, and most of your other trace elements get dosed as well with these systems... Cost effectiveness of these additives would vary with quantities bought... 1L of each could cost $20/L while 5 gallons might set you back $150 a bucket...
One downside of using Kalk only is the precipitation of Magnesium... in my system, (Ca reactor + Kalk), I find that I have to monitor Magnesium, Strontium and Iodine, as they tend to fall, especially iodine which apparently gets skimmed away quite quickly. No matter what system you use... be sure to use test kits to make sure you're not over or under dosing. Some of the most successful reefs I have seen are done with NO supplements, rather frequent water changes with water prepared to values of natural sea water... sometimes I think in this hobby... as with computers, that success or failure depends on the wind direction....
This is just from my own humble experience and in no way to be taken as an "expert" opinion... do LOTS of reading... Emily B has posted some very useful water chemistry links.