Sorry if this has been asked before, but I'm curious. Do paid library effects work in the free version of Nebula 3? And if not, how expensive and difficult is it to upgrade? All I'm seeing on the site is a Nebula 2 Bundle, which I can easily afford and a Nebula 3 Pro Bundle, which is totally out of my price range.
By and large they do not work in the free version. There may be a couple of demos (single programs) which are designed to work in Nebula Free but for the most part all commercial and third party libraries require a commercial version of Nebula.
As far as which version is for you, there are differences. Possibly one of the most significant is that some modern compressor programs (of which there aren't that many yet but it's a growing collection) require the engine upgrade that is only available in Pro. I believe most other programs should work in 2, 3 or 3Pro/Server.
Do some searching in the forum, this question has come up before and you should find some precise info to guide you.