The cheap ones actually use a dvd-rom drive I was told by a sony rep, hence their compatibility
Absolutely correct. Cheap DVD players typically consist of nothing more than a stripped-down IDE DVD-ROM drive (usually by someone like Cyberdrive), and two circuit-boards, one at the back (video hardware, generally PC-based as well) and the front panel (usually just a few passives and a display, and even the display now is being left out of some cheap players -- who needs it anyway).
I will only buy cheap DVD players now due to their superior compatibility. And when I say that I'm not referring to Apex etc but truly non-branded stuff. Mustek are particularly good for compatibility, unfortunately they can be very unreliable.
I have settled on Yamada players for now, but I have a feeling this is a brand-name of Umax, a German company, and hence may not be available in the US.
Cheap DVD players are now at the point where they're only pennies more expensive than DVD-ROM drives. I recently bought a Yamada DVD-2500 for 26UKP inc sales tax; the Cyberdrive DVD-ROM drive inside costs 22UKP inc from my usual on-line reseller......