I pretty much was in the same situation a couple of weeks ago - our storage was close to the limit and the disks reached their end of lifespan. So I went with a 24bay LFF used Supermicro, with Trays, 64GB of RAM, a very nice RAID-card with BBU plus all the trays, dual E5-2670, dual PSU - for just 750,- EUR shipped, including a 1-year warranty. That's a fracture the costs of a new server, you won't save that Money on power costs. (I might pull one CPU, as one CPU is enough for the job). 24x8TB, running on RAID6. Server is running on Windows10 (Desktop), that's good enough for a two-person use with lots of data.