Don't get the Electro 2. The Electro 3 has *way* better piano sounds and allows you to load samples from instruments like the Mellotron.
A controller keyboard would be fairly affordable; it's the virtual instruments, and a host for them, that will be more of an issue. Kontakt 4 might be a good choice; you could use it as a standalone instrument and it'd be easy enough to arrange the samples for all the various keyboard instruments. The drawback is that you won't have drawbar control over your organs, since everything is sampled. I'm not aware of anyone who makes a good organ instrument without sampling though, now that Native Instruments no longer sells their B4-II (what I use when I'm not using organs on the Nord). You'll certainly get a good range of organs in Kontakt though, so if you're not too picky about having the exact drawbar registrations that you want, it'd be the package I'd recommend. It also has a decent set of effects you could use.
Alternately, for a bit more money, you could just pick up Komplete 6 and a host like Reaper (pretty much the cheapest host I'm aware of, if you're a PC user) and then you'd get Kontakt as well as Guitar Rig (for more and better effects, if you need them), and a few synths and such; all good products.
