Long story short, cheap watercooling is going to cost more and cool worse than a good air cooler. GOOD watercooling isnt going to be cheap, but will outperform even the best air cooling. Example...My thermalright ultra 120 extreme only allowed me to put around 1.55v into my cpu and that was when it was around 50F in my apt. Now, my watercooling, i have had as much as 1.6v with it being 80F in my apt. If i had tried to push that kind of voltage through my chip on my TRUE, stuff would have melted.
My video cards used to idle around 55c and load around 75c with their cooker cages. On water i get 35c idle and around 45c load.
My cpu on the TRUE (best air cooler on the market) idled around 50 and loaded close to 65c.
On water i get idle temps around 45c but only load up to around 55c.
Temps will get better though when i make some adjustments to the waterblock. Hoping to get idle temps down under 40.
In order of performance.
Stock/cheap air cooler - free/very inexpensive
cheap water cooling - cheap, but usually more than high end air
High end air cooling - less expensive than water, but better than cheap kits
High end water cooling - not cheap, but you get what you pay for
Phase/NO2/Dry Ice - expensive, dangerous, and requires lots of extra stuff to keep from killing your cpu/gpu with condensation (below ambient temps)
Did i miss anything?
*edit i guess that story wasnt as short as i had planned