How old would you guess this is, and how sturdy compared to entry-level Craftsmans today?
http://sfbay.craigslist.org/pen/tls/2764671795.html
http://sfbay.craigslist.org/pen/tls/2764671795.html
Looks like any of the C'man bottom roll cabs from the late 80's and up.
Likely quiet glide slides. Prolly around $119 to $129 new and $99 if on sale.
Thin top drawer is nice for screwdrivers, but it is an entry level box at heart.
$50 is not unheard of. I'd ask $40 and meet in the middle at $45 if you really want the box.
Craftsman 3 drawer carry boxes are going for $35 used, so $50 is not that bad IMHO.
If slides are kept lubed and used for weekend work it's a good box as I have several that are now the home to countless power tools since the dwrs are so deep.
My big question is where is the lock adn key mechanism for the lock bar?
Unless hidden under the mat (which would inhibit the abilty to add a top box), I;m not quite sure of what I am looking at.
If keyway and lock is at the bottm, then it's likely 80's or pre 80's which means it's a better built box likely.

I think that box had the loop at the bottom for a lock?