I was thinking this too, would be great if we had a decently priced source for these PCBs!
FWIW the CalDigit TS3 doesn't seem to be available anymore, replaced by TS3 Plus (~$480AUD) or TS4 ($??)
I'm also building an eGPU and ordered:
1)
a 'cheap' TB3 M.2 SSD enclosure (M-key, NVMe) ~$110aud
2) an
ADT-Link M.2 to PCIe x16 (x4 electrically) riser
And for extra points, I'll be
adding TB3 to an AMD system (DeskMini X300) with:
3) a Gigabyte Titan Ridge 2.0 Thunderbolt3 PCIe card (with jumper to force power-on, working and detected by Windows but haven't been able to test with any TB devices yet)
4) an
ADT-Link M.2 to PCIe x4 riser
Plus as a test from my ITX machine, I've got a (bifurcated hopefully) PCIe riser to split the main PCIe x16 into 2 PCIe x8 slots to see if I can have my cake & eat it too