A business like what? Reseller hosting? Or free hosting?
Like any business, your initial costs and when you'll begin to turn a profit depend on your business plans. When I started out, I initially paid lessn than $1000 my first year for hosting, billing software, and domains. (I designed and integrated the sites myself, and did all support myself, so I didn't have to pay anyone else anything.) I went with a solid provider, I made sure that I had an emergency-exit strategy, and I kept my expenditures low. I may have been able to make more money faster if I'd marketed more aggressively; but since I never took any marketing classes and since marketing is in fact my weak point, I stayed pretty conservative in that area. I promoted myself within certain channels, got some clients, got some more by taking freelance web design jobs, got friends to refer friends, and persevered.
How big a risk? Uh...well, there's a statistic that 80% of all small businesses fail within the first year. I'd say, just keep plugging away, take small sure steps at first, and have friends with whom you can talk. And plan things out carefully. Many small businesses fail because the owners flew by the seat of their pants, and so they didn't really know how to react when things got dicey.
Sorry I can't give you a better answer. That's kind of wishy-washy. But - seriously - think ahead, plan, and you'll stand a much better chance of succeeding than you would if you just jumped straight in.