Are you planning on taking at least two trips every day?

I'd recommend buying a farecard ($5), putting $15 on it, and re-upping if you run out of funds. The trip from Arlington (cemetery, is that what you mean?) is $1.95 off-peak. Cheapest fare is $1.35.

Use this page to figure your home base station, and then scroll down to get fares to "all other stations" to give you a sense of what your daily ride average is likely to be. There are peak and off-peak charges. If you are not traveling far, your fare is likely to be $2 or less.

I think this is likely to be a better bet than the $35 short trip pass.