Larwee gave you SUCH a good answer!
It really does depend on lots of things including your current skillset. If you don't know how to build sites, do SEO or PPC or market and aren't good at copywriting and have no common sense - well it could take forever to make a dime.
A large majority of affiliates make 0-200 a month. For some of them 200 is a lot to make on the side and they are happy. You could make 200 a month failry quickly if you take the right steps and already have a good foundation of web skills.
Many affiliates consider 5,000 - 10,000 a month "real money". It can take awhile to get that level depending on lots of factors like the ones we've mentioned above.