Well, the best air cooler you can get is this http://www.coolermaster.com/product.php?product_id=6074
The most reasonable is the CM hyper 212 EVO with 2 fans(comes with 1), $34 on newegg, so yes under $50 for a cooler is sufficient.
What does the $80+ Noctua give you over the 212 evo with 1 fan? 1 degree cooler with the c14, and 3 degrees WARMER with the d14. http://www.hardwaresecrets.com/article/Enermax-ETD-T60-VD-CPU-Cooler-Review/1467/6
dont lsiten to this idiot 4.5ghz are u jokeing u shoudl buy the best ones availble for that speed and i listed them if u dont its really realy stupid of u but its your decsison dont make a bad one...
looks like the idiot was right, might want to watch the comments.