How much would it cost to cover the entire land area of United States with dollar bills?

To answer this question, you may find the following information useful: The contiguous United States $($all of the states minus Alaska and Hawaii$)$ can be approximated as a rectangle that measures $1000$ miles north to south and $3000$ miles east to west, while Alaska has about one$-$fifth the area of the contiguous states and Hawaii is small enough to be ignored for this rough calculation. Also, note that a dollar bill measures around $6\mathrm{.}5$cm$\backslash$times $15\mathrm{.}5$cm

$.$

Express your answer to one significant figure.