Last time I got glasses, I tried a test, I bought the $300 glasses from my eye doctor ("only" $200 after insurance), and I bought a pair of $39 glasses online. I found no difference between the two other than price (and the ones I bought online arrived by mail the day before the expensive pair was ready from my eye doctor).
And I bought a second pair of backup glasses for less than my eye doctor wanted for his "lens protection insurance".
Though admittedly, I have a simple, low-power prescription (< -3.0, no astigmatism), so your milage might vary with a more complex prescription.