If Mr/Ms Anonymous wishes to contact me, I can check the gutter etc for him/her. I've checked out friends' places in Chiba and elsewhere. Immediately after Fukushima, prices on detectors rocketed past $1200; now they're back down around $300 and in plentifu supply.
The cheapest sensible devices available in Japan at the moment are probably one of the Soeks range. This is a detector, not dosimeter. It doesn't log data, and there's no PC connectivity, for example.It only runs 10 hours on a battery, though.
For dosimeter, the DosRAE2 is readily available and, again, reasonably priced. It runs 400 hours between recharges and is designed to be worn as a badge. Lots of alarms. The PC software for logging data and managine multiple DosRAE2 badges is laughably bad, though.
If you really want one of these things, I'd definitely go for the simple geiger counter (i.e. Soeks), because you get a very visual idea of what's going on around you. Many of the people using these things around Japan aren't capable of interpreting the results.
Hotspots within Tokyo: not seen anything comparable to yer average granite lobby, and nothing anywhere near, say, Colorado.