Plywood bed floor under $100..

[shp4man]

There's a thread in the 67-72 section about plywood bed floors, but thought I'd post here.
My truck's a '65 long stepper with completely rotten OEM bed wood. It's a patina style truck with good mechanicals but faded paint/some rust

..anyway, the bed is actually about 4 x 8, just like a sheet of plywood.
So have been researching the different plywood grades, and hardware replacement from the cheapest sources.
I figure I can do a good, long lasting bed replacement for under $100. That's with some black or grey paint for the plywood and hardware and rust sealing.
I'm curious to see what it actually costs. It's always more, as you know.