The last plasma I purchased was a Panasonic 50S1, which I got for under $750. This was even at a B&M store. Looking lately, even online, I cannot find a 50" Panny for anywhere close to that price point.
1. What would be considered the S1 equivalent these days?
2. Am I correct in assuming that you will pay ~ $1k for the bottom of the ladder Panny 50? now just three years later??
The equivalent would be the ST50 (S series) but even the UT50 (which is currently 900 at amazon) will be better than your S1.
You might have bought your S1 on a clear-out price or a good sale. 2012 models were just released early this year and have just started going on sale not too long ago. You usually have to wait until later in the year to get really good pricing on current models.