Snap ons are good, but you only buy a half set for $40. Even SK set is $50-60.
That being said, I would buy only the extensions you need. You might not need every size sold, and that will save you money. 2,4,8 inch will do alot of work. or 2, 6, 11 inch etc.
Just pick your poison and go for it. The in-between siZes are a luxury, and you are on a budget, I'd get good steel and fitment first before 100 sizes.
Proto is alot less expensive, but subjectively a half-grade below. Williams USA don't have knurling; there taiwain ones are more modern design but maybe not as good steel.
Don't overlook cman usa (NOS) for good mid-range stuff, just buy in person if can.