Hi Rainforest, sorry to hear about your husband.
Anyway, yeah, I'd think it'll sell for $500 for the boxes. Heck, if I was in the market (and in Colorado) I would grab it for that. IF you got a can of car wax and cleaned / polished it up you might get more, tho it has some dings and a couple rust spots... but cleaned and shiny will help. If thre are tools iniside, you might want to separate those out, or sell it as a complete set, tho doing that you'll lose money in the deal.
I have a really similar Craftsman set up (26" wide) that I put new casters on (because the old ones were tiny and really old and weren't really designed to be moved like I needed them to move) and use it as my job box. These tall & narrow sets, I found, are ideal for this, especially around a shop environment where I need more than a taco cart. I can move mine from bay to bay as I need... so yeah. Plus it's a Matco, so even though it's older, it'll hold up. Plus it has the middle section of drawers, so whoever gets it will have a good assortment of tool space at her (or his) fingertips.