Here are some statistics...
http://www.cdc.gov/hiv/policies/law/risk.htmlOn the one hand as a hetero male the odds of contracting HIV are quite low. On the other hand we all hear about needle sharing drug users getting AIDS from each other, and that's only 12x as likely per incident. But then again addicts probably shoot up much more frequently than most of us see hookers. And the density of HIV infection among needle shooting addicts is probably greater than that found among typical working girls.
I guess the bottom line is that guys rarely get AIDS from straight sex. Straight sex with prostitutes is probably more dangerous, but HIV infection is still rare.