brotherhood_of_LAN - 3:03 am on Sep 20, 2013 (gmt 0)
Virtually every host out there has an affiliate program, some giving cash in return, some giving discounts to your own bills with them. Others have reseller programs, where you buy a larger slice of a server and your referrals get placed onto it.
Perhaps an easier way to provide hosting is to incorporate it into your 'package' of services. I imagine if you're dealing with lots of non-web savvy clients, they'll come to you whether it's an issue with their site, or with their server... regardless, you'll have to waste time on it. In that sense, it's easier for you to control the server and deal with issues more quickly, and charge for it (if that's a job you're comfortable doing).
Hosting can be as little as $15/year if you're buying it on a one-by-one basis. VPS' are quite popular and you could easily charge $100 for the hosting while also being in control of the server.
Alternatively, you can buy a dedicated server and place clients sites on it. From what I've seen, a well priced dedicated server is comparable in price to the smaller VPS when you compare cost and hardware.