Those cheaper dvd's are most likely bootlegs.  
The bootlegs I've seen have been VERY poorly 
translated (Japanese -> Chinese -> English), 
terrible image quality, and no extra's.  This has 
changed recently, but supporting bootlegs is not 
the moral thing to do.  If you are referring to 
the few licensed R3 HK dvd's (ODEX, mostly), I 
would suggest buying them if it's cheaper.  While 
not having great subtitles, ODEX releases 
generally have terrific picture and audio 
quality, since they recieve masters from 
Pioneer/Bandai/Whoever directly.

---Fireye
(And if I've misread your message, sorry)