If the intel stock CPU coolers are sometimes faulty, whats the cheapest 3rd party cpu cooler that will adequately cool an i5 2500K that isn't overclocked?
If its faulty, you should send it back. That being said, I can not look in your wallet so I dont know what you find cheap. But the Hyper 212 Plus should cost around 25$ and is reviewed as one of the best price/performance coolers. Or you go with the more expensive, but also more silent Mugen 2 Rev B. There are more options, but these both get great reviews. (I can say that I love my Mugen 2, its cool and silent ).
On a side note: This is not really the topic to ask these questions in.