Reddit mentions of PCI-E Extender Riser Card Express USB 3.0 1x to 16x Adapter with SATA Power Cable & LEDs for BTC Miner

Total came out to ~$400.

Case $93:

BestDuplicator - Premium 9 Bay Case

Bays $65 each:

3x Kingwin Aluminum Five Bay Hot Swap


Drives:

8tb EasyStores, already had them all and prices varied over the different sales BB had.

Then I'm using an HP SAS Expander I bought off eBay for $18, and powering the card with a pcie extender that people normally use for GPU mining. (Card just needs power, not data, so it works out really well)

Various SAS cables I already had, etc.

Whole thing is just one SAS 8088 cable, super easy.

Here's the PCIE extender:

PCI-E Extender Riser Card Express USB 3.0 1x to 16x Adapter with SATA Power Cable & LEDs for BTC Miner

You can definitely stick with the Fractal series. I did because I couldn't have a loud, unsightly machine setup anywhere in my home. I have my main system w/ 10 Drives + 2 SSDs + 3 NVME drives in an R6. That has a DAS connected with 19 drives inside an R5; 8 stock bays + 3 in 2x5.25 bay adapter + extra 3 drive cage + extra 5 drive cage.

As you are in Europe, you might not even have to pay crazy shipping charges to buy spare drive cages from https://www.fractal-design-shop.de/Define-R5_1. In the US I had to source the extra drive cages from r/hardwareswap but that proved to be easier than I expected. Here is a pic I took before I added the 2nd 5-bay drive cage: https://imgur.com/a/TWL8IB1

Edit: Request for more info...

I have not done a build log as I am not yet "finished" with the build, but it looks like there is sufficient demand for parts info so here it goes:

I have an R6 for my main NAS server loaded with the motherboard, 10 3.5 drives and one SSD. The R5 has two extra drive cages (3 + 5) as well a 2x5.25-to-3x3.5 bay adapter.

The expansion cards I use are:

• 1x LSI 9210-8i with SAS to SATA cables for 8 of the 10 internal drives in the R6. The other 2 + SSD use SATA ports on the motherboard.
  
  
• 1x LSI-9207-8e connected via 8088 cables to two HP SAS expanders powered in the R6 by riser cards which connect to the drives with the same SAS to SATA cables as above.
  
  Additional parts I used:
  
  
• An SFX PSU is important so you can fix the extra drive cages. Don't skimp on this one. You don't need a ton of Watts (I'm using a 600W Gold) but you need quality, you are hooking up thousands of dollars of drives to it!
  
  
• Power splitters: One & Two
  
  
• Power switch to turn on the DAS PSU and reset it any time you need to take the NAS offline (DAS always must be powered on first)
  
• Fan controller for powering fans in the DAS
  
  More inspiration can be found here: https://www.serverbuilds.net/16-bay-das

You'll be looking at something similar to this. There's lots of variations of these mining risers out there but whichever you get I highly recommend you get one with a 6 pin PCIe power plug and avoid molex plugs like the plague. Also don't use the included adapter, plug in the 6 pin straight from the power supply and you'll avoid something catching fire.

Pretty much this. There are lots of cheap HP 24 Port PCI-E 3Gb SAS Expanders on ebay and some are even sold with cables, but probably not the cables you'd need. You'd probably want Forward Breakout Cables. You also need a way to power them and there are PCIe power attachments, that are commonly used on mining rigs, might work. I think the USB portion is only for data, so you'd need to find cables for molex to sata (15pin?). You could use 3-4 HBA expanders into a cheap external port card like 9200-16E. You'll also need multiple power splitters to spread power to all these HDDs.
https://www.ebay.com/itm/New-HP-SAS-Expander-Card-24-Port-SAS-PCI-E-Expander-Board-468405-001/171532956108
https://www.amazon.com/Cable-Matters-Internal-SFF-8087-Breakout/dp/B012BPLYJC/
https://www.amazon.com/dp/B073RBP3V6
https://www.ebay.com/itm/372102178384
https://www.amazon.com/gp/product/B0086OGN9E/

Are these 2.5 or 3.5 HDDs? Without a case the 3.5 HDDs will vibrate and probably can cause connection and data issues, so definitely have a backup and expect the HDDs to quit working here and there. This is also rather power consuming for how much storage space you get.

Even though the price of data cables, expanders, power cables start to creep up, I still think if you construct your own case then it would be cheaper than anything prebuilt. Buying anything to hold the drives would be costly, even buying 12 of these to hold 48 drives would cost $204 alone and you have no cables or anything. Some have built their own by fastening metal brackets together (standalone or within select cases), but this lacks rubber needed for vibration protection... This also doesnt account for how you'll cool the HDDs, but perhaps one big fan could get you by. Post some updates and pictures if you decide to commence on "Project Janky", gluck.
https://www.amazon.com/Rosewill-5-25-Inch-3-5-Inch-Hot-swap-SATAIII/dp/B005FHHOXE
https://imgur.com/3xsabQU
https://www.reddit.com/r/DataHoarder/comments/aceglg/new_build_in_progress/