Well, you can't get much cheaper than this for $3 shipped:
http://www.dealextreme.com/details.dx/sku.1137
It's a little dimmer than the nite-ize minimag drop-in, but pretty close the Inova X1 in both output and runtime on 1AA. Don't know if it will handle lithium batteries, but on a 2200mAh NiMH I got almost 7 hours runtime to 50% initial output.
I know any light can disappear quickly in an office setting, so the cheaper the better for lights not locked up, IMHO. Both dealextreme.com and kaidomain.com have plenty inexpensive lights that might fit the bill. You can get several luxeon clone AA lights for ~$5-8 shipped at both sites (including the very popular "ELLY" model which I know can take a lithium AA). You can even get that one with a much brighter cree LED for under $10 shipped!
Unfortunately, runtime is low on most of these 1AA luxeon clone lights for your application (and high brightness would just encourage people to walk off with them!). You can also get a MXDL luxeon clone that runs on CR123 for $6.50 shipped at those sites, but again I expect runtime would be somewhat low (although use of CR123 might discourage theft).
I still think the floodier multi-led setups would be your best bet in terms of cost/runtime/theft prevention.