I have some cheap hi power magnifiers for close work.

We have those at work. Really useful. But the double-glasses thing is more for when I have to thread a need at home, stuff like that. And I always have a pair of folding glasses in my backpack, because you never know.

Have you tried some of the online shops like Zenni? They were half the cost of going to an optical shop, with the same features.

No, I went to my local optician, for one reason: I only had the lenses made to order, and the instructions for making them were rather precise because they're mounted in 3D-printed frames I designed myself. Also, I wanted Trivex lenses made specifically by Hoya and nobody else.

So my local opticial took care of ordering the blanks from them (you can't order direct from lens manufacturers, sadly) then having the blanks edged with my template tool and explaining to the shop how to use it. It's not that any of this is super complicated, but if anything went wrong, they were on the hook, not me.