Given that the majority of the mp3 players (in sheer numbers, not number of brands) out there can handle VBR perfectly, it will take a masterstroke of unluck or stupidity (aka uninformed purchase) for one to buy an el cheapo that can only handle CBR.
If the iPod can't play VBR perfectly, dump it.

If you're concerned about VBR you'll be getting something renowned for its sound quality anyway (Creative, iRiver, iAudio, etc).