Advise on a Cheap NAS Build

Hello all, I'm trying to build a home NAS, mainly for backing up pictures as well as making occasional back-ups/restore points between windows and mac devices and am unsure what parts I should get and what software is the best to run the NAS. I will be using two 2TB 2.5" drives or two 4TB 3.5" drives depending on the case I get eventually. For now I'll be using an old mITX case with plenty of drive space and support for an ATX power supply.

For the list of parts I currently need is a mITX mobo, ram, CPU and any suggestions on HDDs I should put in it(but don't include them in the budget). I have a case (for now) and a PSU for the build. I'd like to buy used parts unless new is the way to go, and in the past used parts seem fine for my daily use. My budget for this build excluding HDDs and case is 100$. If the budget makes me crazy let me know, I don't have any experience in building a NAS.

Here are some of the parts if been looking at on eBay:

Mobo-
Opt 1: https://www.ebay.com/itm/311793781697 40$
Opt 2: https://www.ebay.com/itm/132090758846 60+6=66$

Ram-
Opt 1: https://www.ebay.com/itm/391696448632 8$
Opt 2: https://www.ebay.com/itm/282380764530 13$

CPU-
Opt 1: In mobo^ 0$
Opt 2: In mobo^0$

All in-
Opt 1: 48$+tax
Opt 2: 79$+tax

I appreciate any help you folks may have to offer!

For that price, you might as well just get a two bay prebuilt NAS from say Synology, QNAP, or the likes. Cake to set up and will take next to no power.

Really? What's the difference between the two?

I still believe that if you want a NAS for minimal use or archives or backups, and your budget is below 200, then, you're better off as Blue Fox said. A 2-bay NAS is about 150-ish, and you won't need to do any of the installation except for plugging the HDDs and power. The software or OS is pre-installed, you just need to configure it to suit your needs. Using other free software or OS, like FreeNAS or etc may add some complication when you're in a tight budget.

Also, the option 2 memory isn't compatible with your option 2 mobo. I can't remember if the ECS Kabini boards were ever made compatible of Registered ECC modules.