To quote a friend of mine, there are only three reasons to use watercooling:
1) You have a furnace, and air just isn't cutting it. 2) You want a quiet computer. 3) You like tweaking things, and think watercooling is (mind the pun) cool.
Based on the initial question, I think we can strike item 3, and based on the notion that it's "only" $25 extra, you probably aren't looking at something likely to achieve item 1, possibly not even item 2.
If you're going to use water, you need to do it right. That means a three-digit price tag, really.
If you really like to tweak, then you may cool it with oil ^^ --> http://www.tomshardware.com/2006/01/09/strip_out_the_fans/