The price was $23.95! Not exactly sure of the date, but by any reasonable estimate, a lot of money at the time...
I just took those pics out on my front steps the other day, before the rain set in. Yep.....as you guessed, there's a totally stock red/white/blue striped Hodgman "Float" that came with that box!
It's one of the "crown jewels" of my mat collection. At the same time I received both this mat, and a smaller kid-sized mat, in their factory boxes....a rare score indeed! If you're curious about what it looks like, it's identical to the Hodgman postcard pic I sent.
The date is mid to late 50's on this long-striped Hodgman!