Fitness Babe Cara Castronuova -- Hell, I'll Date Anyone ... For $10K

Fitness guru Cara Castronuova isn't very discriminating ... she'll go on a date with ANYONE who's willing to pay the asking price -- $10,000.

Cara -- an ex-trainer on "The Biggest Loser" -- tells TMZ she's raising money for her charity -- Knockout Obesity -- by offering a romantic evening in NYC with anyone who ponies up 10 grand.

The best part ... she's open to men and women.

Cara says she hopes to go on at least 3 dates so she can send 50 overweight kids to fat camp. She's moved by the heartbreaking letters she gets ... including one from a boy who told her he desperately wants to shed lbs so other kids will stop pinching his stomach.

So what do you get for your money? Cara says the date consists of dinner at a really nice place and then seeing the new Rocky musical on Broadway.

But here's the deal ... you have to pick up the tab for dinner ... and pay your own way to NYC. She'll take care of the theater tix.