I don't think that economy would be a proper word for Vai's sound, since he must have a 50000 bucks rig!!!
But having an Ibanez with good humbuckers is a good start... I have heard that he uses a boss DS1 distortion pedal (it's also Satch's favorite) as for other stuff (delay, reverb) he uses a piece of gear from eventide, that costs around 7000 bucks... Uses his wah, from morley (the bad horsie) and use his "ten hour workout" then, you'll sound close to yourself trying to play like VAI, since 90% of your sound is in your fingers...
Good luck...
(just saw him in France, and it appears that he has a lot of bass in his sound, but only when his tech plays through his rig, when he does, the sound is perfect... weird huh??)