Collecting them can be confusing as there are many variations. Billy Williams has three different versions. I was recently able to add all three. They were auctioned on Ebay and I was the only bidder for all three. They cost me about five bucks each, which is pretty reasonable.
The three versions are also listed on the PSA master set, so I knocked off three more. My completion rate is up to 79%, 113 out of 143