Each family will be different, and their approach will be influenced by the bride. Have many long conversations with your lady about what she and you want, and agree it clearly before engaging in a negotiation with the parents!
I've had repairs to my specs, then a sight test, and a new prescription. A regular clear pair of varifocals put in my own frame and a pair of prescription sunglasses in a new frame. From an optician who operates from a stall in a large market, but who brought the finished products to my home. Total cost about 7,000 baht. That's maybe a third of the cost for the same glasses in the UK
Thailand is not interested in how long the IDP is theoretically valid for. After 3 months Thailand requires you to get a Thai licence. It's not like it's difficult or expensive 🤷♂️