My guess is that few (if any) make any salary whatsoever. Sponsors give them contingencies and cover travel and operational expenses. Plus they collect the earnings of the 10-20 races they compete in annually.

I can't imagine it is lucrative.

+1 Yes, but those earnings are paltry. It 'costs' more to get to the races than the some of the winning pay out. Look at the purse at the races. A 3rd place IM finish might pay $2,500. If you had to pay for it yourself, which 99% of us do, an IM trip can easily eat-up $2,500.

http://www.duathlon.com/articles/3264

If I am correct, a "purse" is the total amount paid out to all winners (OA and AG). Kona pays $100,00 to #1 OA. And something posted here at Trifuel from 2005 supports this. Scrolling through the IM purse money from '05, most of the #1 OA pay ~$10,000 or so. Might sound like a lot, but how many can you win in one year (much less over a career). And if IM is the only race in the five-figure payout for winning, these other races are obviously paying a fraction of that. Other than the first person across the line each year at Kona, I can't imagine there are any others making six figure incomes from race wins. Maybe that income is possible from sponsors, but at best those slots are reserved for the heavyweights. I'd guess a highly competitive PRO male (one or two IM wins per year, top 10 Kona) may make $50,000 USD per year (wins, endorsement, consluting, coaching).

Whoever has a good day in Iowa on both the Men's and Women's side nets $200,00 for 1st place at the Hy-Vee Triathlon ITU Elite Cup. Heck, $50,000 for 2nd place isn't too shabby either.
http://www.hy-veetriathlon.com/article.php?story=itu.awards&query=event%...

There aren't a lot of races like that so now days they are getting most of their money from sponsors.

You can listen to the Chris Legh talk about money on Episode 163 of the imtalk.com podcast.