This is a battery tray for a full size 1966 Canadian Pontiac. It is unique to Canada because of it being passenger side mounting vs. the US models being driver side.

It has pitting but no rust through, no soft spots. It's still nice and solid. These are often rusted out, so if your tray is, here's a good opportunity to replace it. 

$20 plus actual shipping costs which will likely be around $20.