In my opinion, an ATO is worth it, as you say it gets tiresome to add water every day, imagine doing it every day for years and years?
They are all roughly in the same price category, roughly about $90-$120 for the "nano" ATO's. There are several good, reliable brands you can buy in this price range. Tunze nano ATO, and auto aqua smart ATO are 2 that I've used, but there are others, there are lots of threads reviewing different nano ato's, you can find them with the search function.
If have corals, or plan to get corals, an ATO will help keep them happy. Same with the API test kit, its not accurate enough for corals, but for fish only tank it's sufficient.