I found Anna on Craig's List, www.craigslist.org, in the rideshare section.
We took the southern route across I-40 to avoid the Rockies in the winter. Total mileage from San Jose to Washington DC was just under 3000 miles.
Her car got about 25 miles per gallon, and we used regular grade gasoline which cost between $0.94 and $1.99/gal, averaging around $1.17/gal.
My expenses to DC were $70 for gas, $15 for food, $6 for an oil change, and a few dollars for phone calls.