That's quite the contradictory statement. You admit air cooling is cheaper than water, but yet still believe at the same price water is better. How's that going to work?
Based on the fact that water has a greater capacity for removing heat from a system. Hence why any system in the world that produces a large amount of waste heat uses water to cool or as a transfer medium. For example, nuclear (other than also being a neutron moderator inside the reactor), other power sources like coal, and automotive applications.
Furthermore, something being cheaper doesn't mean that it is better unless you're only looking at it from a cost perspective.
This pretty much says it all:
Corsair Hydro H80i GT / H100i GTX review: sexy watercoolers - Test results: Cooling at maximum fan speed | Hardware.Info United States
Something like a Corsair H80i GT can best a Noctua NH-D15 by all of 1.5C and it comes at the cost of an extra 14dB of noise. Sign me up!!!
The H75 is an inferior cooler to the NH-D15 and is still noisier. Yup, watercooling sure is king!
It also says that most water coolers perform better (i.e. Better cooling, which has nothing to do with noise) than all but the highest end air coolers. Those air coolers are not at the top of the performance list either.
The H80i GT performs better at cooling than the noctua, in a smaller package, at the same price, but at the cost of some increased noise (at max speed). That article even shows all of that. You're right, water cooling is king!
There are advantages and disadvantages to both methods of cooling, it just depends on what you are looking for in your particular application. If we can only pick from that list and you are looking merely for the quietest cooler (
at full speed), and you have a case that is large enough and a mounting solution robust enough then one of those air coolers might be what you want. But you're looking for the best cooling performance in a smaller package, a water cooler will beat the air coolers any time.