@giddyup
"Quality" (western standard) upvc windows will cost you an arm and leg, relative to the cost of other house components.
That's the reason why just about every house here comes with cheap aluminum windows.
There are quite a few companies around that you can ask for a rough quote, especially if you're in/around Pattaya.
For example:
https://europvc.co.th/
https://www.hevta.co.th/
https://www.tradeupvcwindows.com/
http://deku-upvc-windows-thailand.com/english/
The alternative would be the much cheaper Thai standard upvc windows, but those won't be that much different from your aluminum ones other than the frame material.