I think this was the most recent semi thorough discussion. A quick forum search pulled it up. There were several numbers thrown around with some being verified private sales figures.
www.elitefourum.com/t/full-art-pikachu-trophy-cards-2014-2016-also-2004-2012/15252/1
Obviously prices have come a long way since then. I have no idea how much that would have affected the prices of such obscure items like these.