Well....there is a difference in balls, but it really boils down to a few specifics...cover material and spin. Most new golfers really do not benefit from the more expensive balls..particularly because they are meant to spin more than your average cheap ball. This really hurts the long game as you can add extra side spin to your game. The benefit is of course around the greens, but of course you need to have a good swing to benefit from this too. I have played in the past 3 years a total of 12 different types, and in general they all have pros and cons to my game.
For my game, i like balls that tend to spin a good bit, but that are not that spinny of longer clubs. I tend to like NXT's, Tri-speeds, E6's, and Gamers....these fit my game well. I have palyed with ProV1x, Z-Starx, and 2011x, and they all are great around the greens, they provide a great deal of spin, and putter feel is amazing, specially on the 2011 (I was not expecting that BTW). But when I started playing with AD333, DT Solos, Mojo, pinacle gold, and a few others I can't remember, Iand I tend to like the AD333 the best in this group.
I think that as a rule of thumb you should look to make your selection based on your handicap:
25 or More ~ go with anything you can get for $20 or under (The Gamers are $20/dz and they are great balls!)
15 to 25 ~ go with anything in the $20 - $30 range (E6 / NXT / Tri speeds are good options, but have different feels)
Less than 15 ~ jump into the $40 + range.
I have bought most of the balls that I have tried from lost golf balls, and their 3A and 4A rated balls are tipically in great shape. I was able to test different options at lover cost than retail going this route.
I hope this sheds some light on ball selection...