A lower priced oil doesn't mean it's not as good.
I absolutely refuse to pay the ridiculously high price for Polaris PS4 oil. It's something like $8 per quart (maybe more).
Since I got into quads early last year, I have been using nothing but Castrol Act-Evo 10W40. It's a synthetic-based oil (you can't run pure synthetic in quads because of the clutches), and being the Castrol brand, I trust it every bit as much as manufacturer-brand oil, or maybe even more. And I only pay $16 for a four liter (roughly 4.5 quart) jug of it. That's two oil changes on my Predator or Grizzly, and 1.5 changes on my Arctic Cat (which takes like three or three and a half quarts -- go figure).
Some people are nuts about using nothing but Redline oil for their cars. I think Mobil 1 works every bit as well and is almost half the cost. I think this is a fitting analogy.
Rob