Depends on the year and the condition. If you are talking about an aircooled one and just want practicality, get a late model (mid 70's) and make sure the heads don't have a dropped valve seat. If you don't care if it's a true "vw bus" then you can get the even later Vanagon that will probably be more comfortable and have a few more modern amenities (like heat, etc..).
I'd say you're looking at about $5,000 (US) or more for one that runs and looks well. Maybe even upwards
The classic ones (1967 and earlier) are more collectible and will cost much more, but they are ohhh so nice
Oh yeah, make sure you have a toolbox.
