I may be able to answer one of your questions, but this answer is assuming that you do have a source of authentic knowledge when it comes to saijutsu.
Is there any 'MAJOR" differences between the $25-30.00 sais and the $50-60.00 sais?
Yes.
The $25 sai will be good only for decorative purposes. Typically, these are horribly balanced, and you can't even do proper sai technique with them. Most of the time, they'll have some extra cosmetic adornments, such as a plastic red jewel, or maybe have a decorative skull on them, either on the pommel or the guard. You absolutely do NOT want to be learning on these sai, since you'll develop terrible fundamental technique that will be very difficult to correct.
The $40-$60 sai aren't nearly as bad. They're going to be made of a soft cast steel, and will be reasonably balanced to the point where a decent instructor will be able to teach you proper mechanics with these. They're all going to be about the same, regardless of what your source is (AWMA, Century, Karate Depot, etc). They'll also come in either the regular weight ones, or the "demonstration" ones. The demo sai are a bit lighter, and slightly better balanced.
You're really not going to see anything better, until you start getting into the mid 100's, where sai from Shureido or Kensho have much better balance than the $40-$60 sai. For someone who has had a good bit of authentic saijutsu experience, and has a decent set of mechanics, he can certainly reap significant benefits by using a premium pair such as these.
The next tier starts around the mid 200's, where you can get a pair custom made from someone like Phil Worbington. If you feel that you're ready to reap the benefits from a customized pair, then I strongly encourage you to go for it.