Did you forget to include the motherboard in the estimate?

I’d say $675 if you add $100 for the motherboard.

$120 listed on Amazon

Used I expect a huge discount. Previous owner could have mistreated the hardware and there is no warranty. $300.

If you’re trying to sell it to geeks, build it up in PC part picker, send the link out with the advertisement, and then sell it at 40%, maybe 30% of the new value.

If you’re willing to do hand holding, you can sell it as an entire system, to somebody technically non-savvy. Higher margin, more work

If you’re lucky you may be able to sell it for $575 but the more realistic price is around $500