This link was originally posted by Surfref on the old form. Its very insightful for for any collegiate sports. For the list of sports the database exist for, just remove the soccer.html below and you'll get to the home page.
For soccer, its 5.7% for men and 7.2% for women (across D1~D3 combined). In other words, roughly 5~6 players out of 100 HS boys and 7 players out of 100 HS girls get to play in college.
When you break that down to a typical HS varsity team, its just a handful of players from every 4 high schools, since typical roster is 25 or so. In boys side its probably worse for high school players since much of recruited players are DA players who don't play HS soccer.