While it's true that there are only a very few manufacturers of trinitron tubes, don't underestimate the importance of the so-called "packaging." The brand-name company (Compaq, NEC, etc.) provides all the electronics that drive the tube, and these componants are at least as important to picture quality as the tube itself.
About cheap monitors: The budget brands produce SOME really good monitors, but the quality tends to vary more than with the expensive brands. For some reason, monitors are famous for having variation. Two monitors of the exact same brand and model can have very different visual quality, and the the budget monitors seem to have lower standards on what makes it to market.
This leads to my main point... I would HIGHLY recomend that you view the exact monitor you are going to buy and insist that they sell you that very one, not just the same model--especially with budget brands. This of course means buying locally, but I've found that with the shipping charges on bigger monitors, the price difference between online and local retailer is little or nothing.
Just my 2 cents worth