I've tried a bunch of cheap online vendors (Zenni, Optical4Less, Goggles4U) over the years. All were acceptable and probably averaged about $40/pair total with high-index lenses, but the frames always felt cheap and occasionally I'd get a pair that give me headaches (I later learned that likely either the pupiary distance or optical center were off).

When I did have an issue, the return process was pretty tedious and annoying, so I usually just ended up eating the cost and dropping the glasses in a donation bin.

After a few years, I probably ended up spending roughly the same as if I'd gone to a local shop with the advantage of having spare glasses with the correct prescription for the first time in my life.

Recently tried Warby Parker and although they seem extravagantly priced ($95/$120) compared to the others, the quality of the frames were noticeably better and the customer service in a completely different universe. I had to return my first pair from them since the frames ended up being narrower than I expected/gave me headaches and the exchange process was incredibly quick and painless.

I will say, for anyone thinking about ordering glasses online, try your best to get your pupiary distance measured by a professional. It's not easy to get opticians to do anymore, since they know you are going to buy your glasses online but it's a difficult measurement to get yourself and being off by just a few mm can cause headaches.

[edit - got the price of WP high index lenses wrong]