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 5 1400 4-Core Desktop CPU (YD1400BBAEBOX) brand-new condition for $146 with free shipping. Retail price: $170. Frequency: 3.4 GHz precision boost, 4 Cores/8 threads Unlocked, Cache: 2 MB / 8 MB (L2/L3).
Has good Amazon Reviews.