Especially for a business app. My product <shamelessplug>http://userping.com</shamelessplug> is my first bootstrapped company, and while I'd love to be profitable enough to fully support all the great apps I've come to depend on, right now we're broke, so I have to choose between using your app or paying for another month of hosting. Pretty simple decision.
So, my vote is always for a free option. I think you should feel free to really lock it down and restrict the offerings because anyone who can't afford to pay for a service probably doesn't need 200 user accounts. They probably only need one or two, which should theoretically not cost you very much.
That's my $0.02. I very rarely even try services with a 30-day free trial. I'd hate to get hooked on something that is going to rape my tight budget.