Some sites require more time than others, but most do not require considerable updating on a frequent bases. They go into rotation, with more attention given to the top producers. I use six different hosts for a variety of reasons - which also allows me to keep copies of each site on a different host so that if anything major goes wrong with one host, it is only a matter of changing the dns. The cost is negligible on a revenue/cost basis - a fraction of 1%. I used to be in specialty retailing and there were high profile locations (Union Square, SF - Beverly Hills, 5th Avenue NY) where rent was a large percentage of the expense (over $500K for 1000sq ft.) - the primary reason I was initially attracted to the web. Even the most expensive host is "cheap" unless it is just a hobby or someone is just starting out. Never put price before reliability, speed, uptime, support, etc.
The 1 million dollar question is how do you have to time to do seo and get lots of backlinks for all does sites?