Okay, I’m going to go against the grain here and say “Don’t go with the really cheap online glasses”.
I used eyebuydirect, Zenni, and a couple of others for many years, and was pretty happy with them, especially for the price. However, one thing I’d always noticed is that they’d wind up being pretty beat up with some large scratches in the coatings, or they’d just fail and start flaking off by around the 1 year mark (I’m pretty hard on my glasses, tbf) and I absolutely had to get new ones. I just kind of accepted that I was very hard on my glasses, and that’s what happens.
However, I started going to Costco just because my insurance wouldn’t cover any of the online places, and the quality of the lenses and coatings are absolutely night and day. I’ve had 10 pairs now (sunglasses and normal lenses), and only had one with a single scratch in the lenses, after having them go flying across a cement floor due to me doing something quite stupid.
I don’t think you need a membership for their optical center either, but I’m not 100% sure.