Thanks to this thread and a couple other on here I bought the Onda D1800 to build my first serious mining rig (right now I've pressganged 3 GPUs across 2 desktop into mining). FWIW, there is a seller on Aliexpress that has a pretty good sale going on right now:

https://www.aliexpress.com/item/100-Brand-New-for-Onda-D1800-BTC-Mining-Machine-Mining-Motherboard-Support-6-cards-All-Solid/32829766277.html