Billy was included in the 2015 Archives set. The base set has three parallels and I've picked up two of the three. The missing is the black which is 1/1. I don't expect to ever even see it let alone buy it.
More in my price range is the...
The gold parallels are /50 and I paid $6.50.
I suppose it's supply and demand, but why did these go for so much less than the SSSSSSPs in the base set. The short prints have a run of about 500. My gold Billy is ten times as scarce but wasn't ten times more expensive.