So it depends in how many individual drives you want it, I am from NL so that's where I draw reference from.
The lowest $/TB I have seen have been on 18TB drives new(HC550's) which had an insane deal for 200 euros a piece(For new drives with warranty etc this is basically an insane deal), which means it's 11.1 Euro/TB so the cheapest way to do that assuming you do raid0(so 0 redudancy if 1 drive fails you lose everything) it would be 9 of these drives(162TB).
So assuming you don't want 0 redudancy I would say on an array of 9 drives you would do(depending on what your focus is on you would alter how many vdevs etc) 2 drives of parity(raidz2 assuming your using ZFS/RAID6 in others), which would mean it would put you to 11 drives which would at this "best price" would be 2200.
Generally the best no deal price I have seen is around 300 euro per 18TB drive,so assuming you do that deal the no redudancy array would cost you 2700, and the array with 2 drives of parity would cost you 3300.
Do realise this is dutch pricing, which might vary widely from where your from. And this is buying new and you can generally find recertified drives cheaper while not necesarrily being worse.
Okay so currently my closest matching server would be my R730XD which is running dual E5-2650v4's which should have a similar power profile(the only diffrence with the 2680 is the number of cores however this shouldn't make much of a diffrence for low use workloads).
So currently with 2x SSD's, 2x2650v4's, 128GB RAM, 6x18TB HDD drives, 3x16TB HDD drives my power consumption sits around the 225-250W which over a month for me costs me about 50-75 euros a month in power(welcome to dutch power pricing...). However alot of this consumption comes from the drives, because before I put the HDD's in and just had the SSD's, the RAM and the CPU's it had an idle of around 80-100W. But this is in an enterprise server with some chonky drives so I assume those account for 5-15W as they have a base speed.
Generally I would say unless you specifically need functions that the board provides(alot of PCIE lanes for example) just get a consumer CPU and you'll be much better off as it will have better efficiency, performance and you'll be on a modern platform. And if you go for AM4 it will be really cheap cuz of the introduction of AM5.