Honestly, it just depends on how much you want to spend. A Plug n Play setup that fits right out of the box is easy. For example, Koolance sells a resorvoir/pump unit that mounts right in a 5" drive bay for $139. But then when you factor in the cost of the rad, blocks, and tubing, it can end up around $400.
On the other hand, you could go with an external reservoir, which is cheaper, but then you have to consider other issues like people moving around the case.
It all depends on how much money you're willing to spend.