I would also say don't get the Tornado, T-Zone or White Dot. Those balls will not 'allow' you to advance your game. They are, for the most part, a straight ball and will not get you anywhere but straight. IMO.
I suggest the Ebonites, Hammer, Power Groove, Tropicals are good but personally I'm not big on Roto Grip. There's nothing wrong with them, usually cheaper to go Ebonite, PG or Hammer. IMO, for the best bang for the buck, Clash, Jazz, Vibe or Tropical Storm. I don't know the prices in your area, just the costs in mine and those are the ones I'd tell you to look at before you go into your pro shop, BUT, he/she can see you bowl and you should listen to them.
--------------------
az guy aka: R & L Bowlers Pro
rlbowlerspro@cox.net