The Core i5-2550K should cost no more than $225 which is $9 more from previous i5-2500K featuring base core 3.4GHz with 4 core 6 threads 6MB L3 cache. The i5-2450P price is $195, while i5-2380P is $177 with have similar specification but different base clock.
Celeron B815 have 2 cores, 2 threads, 2MB L3 cache speed at 1.6Ghz with price tag $86. The B720 cost only $70 have 1 core speed at 1.7GHz, 1 threads and 1MB L3 cache.
The Ultra Low Voltage Celeron 867 and Celeron 797 price at $134 and $107 have 2 cores with 1.3GHz also 1.4GHz.