$160 will pay for one of these from United Nuclear. If you can't be bothered with making your own then these look pretty handy.
(http://unitednuclear.com/images/un1503p.jpg)
QuoteThe 1503P indicates levels of Beta, Gamma, and X-Ray radiation by a series of audible 'beeps' as well as a digital display with large, clearly defined numbers on a large LCD display with LED backlighting so readings are visible in total darkness. The pocket size makes it very convenient for industrial, covert & general use. The 1503P will even fit in a shirt pocket. Typically Geiger Counters have a separate probe requiring 2 hands to operate the unit. The all-in-one design of the 1503P allows you to operate it with one hand leaving the other free.
The unit takes two ordinary AAA batteries and the battery indicator lets you know when they need replacing. The 1503P features an industry standard Halogen-quenched thin-wall metal Geiger-Mueller tube.
http://unitednuclear.com/index.php?main_page=product_info&cPath=2_78&products_id=1042