It is entirely possible to start with a 2-bay drive rack (not a caddy, we want something without the connections) and then run the SATA out the back of the computer to the drives. It’s a compromise for this low a budget, but it’s not a major sacrifice.
Older thinkpads in this price range will not perform well as servers. They will be pretty limited in specs. Better to go with a used SFF or other form-factor business model desktop.