I recently bought an HP 2512 just for decals. It was on sale for forty bucks. I bought it with the idea that I could return it for ANY reason within two weeks, so as soon as I got home I made a set of decals and they worked fine.
My normal printer is an Epson XP600, and the inks for that printer run with almost any overcoat. I have had good luck with older Epsons, but not with that one! Problem is that printer mfgs often use different types of inks with different model printers. So I recommend making sure there is a generous return policy, then buy a cheapie that looks like it will do the job, try making a set of decals, and see how they turn out.
I didn't worry about ink costs for a dedicated decal printer because I figured I would not be making THAT many sheets of decals, so believe the cost of even expensive inks will not be a factor. Homemade decals will always be cheaper than storebought ones :-) I often combine a couple of sets of decals on one sheet when I can, to save wasting decal paper (I find the paper cost to be more significant than the ink (this of course would not be true if the decal printer were my everyday computer printer.