looking for video cards for AI server

hi i wanted to buy a videocard to run in my unraid server for now and add more later to make an AI server to run LLMs for SillyTavern and i brought a MI50 from ebay witch seamed a great value the problem is i had to return it because it did not work on consumer motherboards and since it didn't even show up on windows or linux so i could not flash the bios

my goal is to run 70b models (when i have enough video cards)

are my only options used 3090 and what would be a fair price those days?

or 3060s?