eBay has the Intel Core I7-7700K 4.2GHz Quad-Core Kaby Lake CPU (BX80677I77700K) for $310 - $15 off with coupon CSAVE15OFFMARCH (Ends 3/20 at 8PM PT; requires Paypal) = $295 with free shipping. List price: $350. Features socket LGA 1151, intel 200/1001 series chipset compatibility, intel HD graphics 630, intel turbo boost 2.0 technology.
eBay has the AMD RYZEN 7 1800X 8-Core Desktop CPU (YD180XBCAEWOF) refurbished for $318 with free shipping. Features 16 threads, 4GHz max turbo frequency, 4MB L2 cache, and 16MB L3 cache. Features 16 threads, 4GHz max turbo frequency, 4MB L2 cache, and 16MB L3 cache.