I am not 100% sure (been awhile since I looked around) but most if not all glass toys found here are Borosilicate
(pyrex) glass. As such they have the same basic qualities you will find in cookware. These toys are at the top of list in terms of safety. Anything else is sub par, that's not to say they are not still good toys but they will not take the same abuse. (See Test one of Pyrex
and Test #2
Now, there is also two basic ways of molding the glass; by hand and by placing the molten glass in a mold to form it. This is pretty much why there is such a price difference between toys. The high priced toys are made one at a time by the artisan and you are paying for his/her expertise. You will also find the higher priced glass will have more colors/designs molded into the glass versus the cheaper ones.
Hope that helps a bit, if you see something that I am missing let me know and I'll take a look and tell ya what I know.
One last thing if I may, always check your glass before use no matter who makes it or the price. Small scratches may feel alright to the hand but can cause micro-abrasions to delicate tissues and may lead to cracks or breakage. When in doubt, toss it and get a new one.