No need to buy fancy meters - it's possible to build one yourself using readily available household materials - tape, paper, thread, foil, etc.
Kearny Fallout Meter (KFM)
http://www.ki4u.com/free_book/s60p792.htm
http://en.wikipedia.org/wiki/Kearny_Fallout_Meter
As for radiation exposure - the biggest threat from nuclear disasters, such as is occurring in Japan, is not the level of radiation per se, but rather the fall out - ingested radioactive material, even at very low levels, is often far more dangerous...
Often the authorities gloss over that by comparing overall radiation levels to that of background radiation, cross-country flying, etc without mentioning the real danger isn't overall radiation, but type and source of it - ingested radioactive material (fall out) is what causes much of the problems.
To digress, the TSA plays the same PR game - comparing radiation exposure of the naked scanners to that of cosmic radiation one naturally receives flying ... but the TSA neglects to mention the difference between full body exposure and concentrated near skin exposure...
Naked scanners don't take a snapshot like an x-ray machine does, but instead uses a concentrated beam that scans back and forth across the person's body to form an image. When operating correctly, can be relatively safe. But there are risks: the beam being too strong (naked scanners are poorly maintained); the beam remains at any one spot for too long, one can be overexposed (even burned!); the machine operator (TSA agents are
not medically licensed to operate radiation equipment) uses higher resolution / zoom and/or does repeated scans.
Ron