The Uniden 246t is the smallest scanner i own. It can easily fit under a shirt if you use the belt clip, or in a jacket pocket. The only other scanners i know of that are roughly the same size are the the RS Pro-84, the Uniden BC92xlt, BC95xlt, and the BC72xlt.
Not sure what you are looking to spend though, as the price range varies quite a bit on those. I found my 246t on ebay new in box pretty cheap, and i believe the 84 can be had for about 40 bucks on ebay also.(also check the uniden webstore for factory renewed, they occassionally have them pretty cheap)
The Uniden SC230 is only $150 factory refreshed here:
http://www.unidendirect.com/itemlist.cfm?cattype=prd&catid=3&filter=Handheld