The cost depends on the difficulty of the subject and how soon the paper is needed.

VOA: special.2009.04.23

And in some cases, the paper itself suggested what the best subject was.

VOA: standard.2010.03.17

Mr. Tito co-wrote a detailed technical paper on the subject with 10 corporate and NASA space experts.

WSJ: First Space Tourist to Outline Trip to Mars

Mr. Tito co-authored a detailed technical paper on the subject with 10 corporate and NASA space experts.

WSJ: First Space Tourist to Outline Trip to Mars

The authors of one recent paper on this subject presented at a great session on climate policy in Denver.

FORBES: Economists Moving Beyond Carbon Pricing