IMHO, the prices vary extremely but if you want to get just a basic pair of glasses, you can get away with a very cheap. I don't wear glasses myself, but last August I accompanied someone to get a pair of new glasses from Fielmann (Wikipedia: 'Fielmann is market leader in Germany and Europe's largest optician').

In the end, one glasses cost 18€ (special deal) and the other one about 57€ (sunglasses, special frame). Given the 2+ hours, we stayed at that shop (sales talk + eye testing + frame adjustments) it was probably a net loss for the company on that day. I know other people who got their glasses for about 700€ from the same shop (more expensive frame + more features (e.g. thinner lenses)).

So it might be that the market situation is kinda bad and is getting abused. Nevertheless, I have the anecdotal evidence that if you are just after a vision correction (and not some fashion accessory), you don't have to pay a fortune (in Germany). This might be helpful to keep in mind when you are after your next glasses.