Vitamin D blood test meters - perhaps by 2012

A good Google search term is " vitamin D biosensor"

As of spring 2010 it has been prototyped and patented

It will probably be too expensive initially to have in your home.

But I can see having it in a pharmacy - where is would be 100X more cost-effective

Many large grocery stores have pharmacies.

And many of those pharmacies have chairs for blood pressure testing

I can imagine going to the grocery store in 2012 and getting a vitamin D blood test for < $5 in <2 minutes

There may be legal restrictions against it, however, so you might instead have to go to a medical facility, fire stations etc.