Yes, the large capacity 2.5" ATA drives got expensive pretty much the moment they were discontinued. The Western Digital 320 GB 2.5" PATA is still available, or was not too long ago: WD3200BEVE
Price is north of $100 these days though. I don't think it ever got below $80. Kind of a tough sale for a Mini that cost you $20.
At this point in time the best solution for 2.5" ATA and 1.8" ZIF/ATA, if one wants largish capacity, is to get the proper mSATA adapter and install a 240 GB mSATA SSD. It's generally cheaper than buying the old stock hard drives with 240 GB or larger capacity.