I doubt very seriously you will find a hosting provider for free that provides the type of FTP space and reliability that you need in order to run a league successfully.
You're probably best off spending the few bucks per month it takes to purchase a hosting account if you want to do it right.
Some hosting providers I've seen that league commissioners have used successfully are:
All-In-1 Web Solutions
http://www.allin1websolutions.com/
Sim Leagues
http://www.simleagues.com/
PowWeb
http://www.powweb.com/