Eventides are very much still in production. The latest model is called the Orville. As for expense, it really depends on what your budget is like. To some people, spending $1500 on a used Eventide is a steal.
With an Eventide you will be able to nail some really great soundind harmonies, but you will never be able to duplicate what happens when you actually play each harmony yourself. Brian May feeds multiple delays into each other and does a lot of his harmonising live. Whether an Eventide will give you what you're looking for is debatable, since the essense of those killer harmony parts is slight difference in vibrato and 'air' you get with each successive pass ... When I'm doing harmony parts live, either we will use two guitars, or one guitarist picks the most important part of the line and plays it and the other guitarist plays the riff beneath it . Most audiences are not that keyed into hearing harmony parts and won't even know what they're missing. And there's only so much you can pull of live, in any event, unless you pull a Maiden and have 3 guitarists ...