Also, there is a cap on the transit benefit that federal government employees receive. The cap was raised temporarily because of the Recovery Act (to $210/month I think) but I'm not sure if that has expired. The normal cap was $180, I think.

I think that your transit costs are going to exceed either cap...If you take the circulator bus from Gtown to Union Station to catch the MARC train, it is $1 one way. Normal one-way fares on MARC trains are $6, although I'm sure the per ride cost for a commuter pass is less.