From what I can find (eBay), the i7-2600K still sells for ~$100 or a little more. A compatible motherboard in the Z68 chipset (etc) thats working, runs anywhere from $80 to $175 or more.
For that kind of money, I would personally advise against it. 7 year old CPU (no matter how good it was/is) and a comparable aged motherboard..... just a waste of money to me. IF you had a 2600K and Z68 (etc) motherboard, I'd continue using it, it's still good for what it is..... but I wouldn't be investing any decent amount of money into the platform in 2018.
Realistically, for not a whole lot more money (vs. middle ground of eBay sold prices anyway), you could have a modern platform that'll scratch your overclocking 'itch' some...
PCPartPicker part list /
Price breakdown by merchant
CPU: AMD - Ryzen 5 1600 3.2GHz 6-Core Processor ($175.77 @ OutletPC)
Motherboard: MSI - B350 TOMAHAWK ATX AM4 Motherboard ($64.99 @ Newegg)
Memory: ADATA - XPG GAMMIX D10 8GB (2 x 4GB) DDR4-3000 Memory ($90.99 @ Newegg)
Total: $331.75
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-04-02 12:01 EDT-0400
I'd full expect to be comfortably >$200 for an i7-2600K and any decent board..... So while it's still a decent bit more money, it would be money well spent IMO.