I am currently looking at the Thermalrght Ultima 90, it looks like excellent value (£24.99 at scan).
According to AnandTech it virtually matches the Ulra Extreme 120mm at idle and is only a couple of degrees off under load.
It is also smaller (better airflow around other components in a smaller case?) and much lighter (460g as opposed to 790g without fan) if you are concerned about overloading your motherboard. I believe it also comes with a backplate/ fan clips.
Using a 92mm/ 120mm fan seems make little difference, so pair it with a Noctua NF B9 (£11.49) for a performance/quiet option or a trusty akasa amber (£4.49) for a cheaper option.