I worked in the industry until a little over a decade ago, putting myself through an engineering degree. The company I started with was bought by LensCrafters, but before it was we pretty much knew the wholesale prices on everything. After LC, LC just distributed stock to us so we didn't follow pricing.
I was always amazed at the markup. A pair of Sola lens blanks for FT28 bifocals was about $3.50. A typical name brand frame out of the Frames catalog was less than $10.00 (ie: Perry Ellis). Dies for UV and tint were several dollars a bottle and would last a few days to a week depending on sales volume. Basically one tint and uv job would pay for most of the dies and UV.
Now, most of those places were in malls, so the rent there is astronomical, that's one thing to consider.
I wouldn't say people are getting "ripped off", but there's definitely quite a bit of markup. A single vision pair with an Rx such that I could use finished lenses, I could edge, uv, light tint and assemble in about 10 - 15 minutes. You'd be paying a couple hundred for that (depending on brand), but I could do it while you wait. And if I did it, you'd be happy (no scratches, gaps, etc). I always take pride in what I do (even now with coding).
So, what's the convenience worth? Depends on you I guess.