Redmine

Hi Friends

I am new to redmine. To use redmine as a project management tool online I think it is free(Correct me if i am wrong). How many maximum accounts can be enabled for a free service online for a year or if paid service online how many accounts for a year and the cost ? To use it as a enterprise version,is it possible? if so, can you pls tell me how much will it cost for 2000 users?

Thanks