Id say If you are building a new pc, then there is no reason to put money into this old one… If you by any chance want to try some overclocking on this platform just for fun to see what kind of performance is hidden, then you should buy a “k” CPU like: i5 2500k/i7 2600k or i5 3570k/i7 3770k.

Used 10/11 gen i7s would provide good value for the price on the used market, but as everything when buying used, it depends on what the seller is asking, if everybody was selling their old rig for what it is actually worth, it would be really easy to say.