Hmm. I'm not aware of any PC Monitors that are 27-29 inch, at least not in a 4:3 aspect ratio. I think 20" is about the largest LCD 4:3 PC monitor you can find (19" are much more common though), and I believe 21" is about the largest CRT PC Monitor you could readily find, though there were some as large as 24" back in the day, the FW-900 from Sony comes to mind, though the price for those can be quite high nowadays.
Now, you could go widescreen, and that would open up a lot of options for screens that are LCD and connect to a computer monitor, but its less authentic, if that isn't a critical factor you should have plenty of options.
That said, I think the tri-sync arcade monitors from makvision are still available, but they are upwards of 500 dollars as well.
These ones, for example. I believe those should connect directly to a computer using a VGA connector. (Said out of stock, but ships April 1st, which is either the worst ship date ever, or a really mean April fools joke

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