At the moment, it's probably more cost effective to go the vertical LCD/OLED TV with physical bezel route, especially for custom builds. You can get a lot of screen for not a lot of money if you don't need a third party to cut the panel down for you.
They certainly aren't cost effective. It would be better if one of the more consumer-focused brands released a more budget friendly option. Still there aren't many large size gaming monitors with a response time that low that are affordable. You'd need to get something in the 40-50" range to get an equivalent usable screen area for old 4:3 arcade games on a 16:9 display.
Someone suggested them as drop-in replacement for 25-27" arcade cabs. Personally, I'd rather put a new tri-sync crt in an arcade cab than any HD flat screen but some people have good reasons to use LCDs.
I can't see cutting down a 16:9 panel and making a custom bezel being a serious option for diy arcade fans, It's a skill-set and knowledge base that 99.9% of us don't have. I have only ever seen it done in the advertising space. You'd have to consider your own time to be worthless to take on that kind of project as a cost-saving measure unless you already knew what you were doing.