Which mainboards are cheap and have 4 pcie16x (electrical) slots, that don't need weird risers to fit 4 GPUs

Because I don't want to spend $4k.

I want to spend $1500 for a card that can run a proper large model, even if it only can do 25 tk/s.

Intel is squandering a golden opportunity to knee-cap AMD and Nvdia, under the totally delusional pretense that intel enterprise cards still have a fighting chance.