I guess they could be called magnetic clip ons. I have terrible vision myself (-6.5) and require thicker lens (which zenni doesn't actually accommodate I had to buy from elsewhere) and I never found the added weight to be an issue. As far at price, I only paid 150 cdn for the glasses which is one of the cheaper pairs I've owned.

Personally I hate having to carry around two pairs of glasses, it's annoying af but if that's what you prefer, you do you.