For only 5, I'd say roll your own. You get most of what you need from Perfmon & server-side traces. Spending money on a tool for so few servers seems excessive.
However, for only a few servers, lightly monitored, Red Gate's SQL Response is a good tool with a very good price. It doesn't have terribly sophisticated historical reporting capability. If you need that, I'd recommend Idera's Diagnostic Manager, but you're going to pay quite a bit more for that.