When I can find multiple commercial products which will basically fit my needs, I've always found that it's very hard to save money by building my own. That's definitely the case with power supplies.
I think most electronics tinkerers ought to have at least one bench power supply that offers adjustable constant voltage regulation and adjustable constant current regulation. It should probably have meters that show voltage and current. There are MANY companies that make many variations on this kind of supply. They come in many quality levels, with many levels of voltage and current capability. My most used unit is my antique linear HP E3610A which I picked up used for a bit over a hundred dollars. That doesn't mean it's the best bargain for everyone, but it meets my needs, and the quality is excellent -- good enough that for almost any purposes, I can pretend it's perfect, at least within its voltage and current limits.
If you want to build a power supply as a learning exercise, it could be a good project. But it's likely to end up costing more and being of lower quality than a commercial supply. It might be worth it if you end up learning enough from the exercise, though.
Having said that, I agree that the 100-120V DC supply for electroplating is a specialized beast. I don't have such a supply now. My inclination, at least to start out for occasional use, would be to use a dozen or more 9V alkaline transistor radio batteries in series, to get the high voltage and low current. In addition to very low cost, it has the advantage that the internal resistance of those small batteries limits the current somewhat. While it's not totally safe, at least an accidental short is unlikely to be as spectacular as shorting DC produced by rectifying mains power without proper current regulation. If I found that I wanted to do frequent electroplating, I'd look into other alternatives.