$.50 per trip sounds about right to me... What do you think the gov't should pay you for taking your bike to work? Last time I bought a tube from the LBS it was $6 even. $20 per month should offset the cost of maintenance to use your bike regularly. It is the cost of lube, tubes, and the occasional tire. In fact, over time it is enough to pay for a chain and cassette as they wear as well.
The purpose of this money is to offset the maintenance to the wear and tear of your bike if you use it regularly to commute. It is not to encourage people to get out of their cars.
I'm not discussing the "bail-out bill", just this part.