Cheap Office Chair Mat?

All you gotta use is a beach mat.
Or a tarp, that you get from a local hardware store.
Anything plastic. Thus easily wiped or hosed down.
OR put down a huge beach towel under them. Then you just take it and dust it off etc.

So you mean to say that, they BOTH EAT while sitting in your Hubby's desk chair??? at the desk?

Or, you make Hubby... VACUUM after he/your son eats.
Make it, his... responsibility.

OR, tell both of them... to ONLY snack, using a food tray.
That is what I do with my son. He's a boy, 6 years old and is messy.
There are many cool/cute food trays. Look online.
My son, will tote his own food tray, to wherever he is or is playing...and he eats/snacks OVER the food tray. And if he does happen to get crumbs on the floor, HE WILL pick it up! If a 6 year old can do that, I assume a Husband can too.
TELL your Husband/son... that if my 6 year old can do that, they can too.
Make them, responsible for picking up all their crumbs or eating more neatly. And get them trays. And tell them they can ONLY eat/snack over those trays. And only put their food on it.

The thing is: whether it is a plastic or fabric or hard surfaced things under that desk/chair... you STILL will get... crumbs and food particles under them where they eat/snack.
So the thing is, make Husband and/or son, responsible for vacuuming under there. Or tell them to eat/snack someplace else.
Or make them wear bibs with pockets in it.

I saw the office chair mats for $20 at Costco

I was going to suggest IKEA, too. but it is a haul up to Frisco, so you could try one of those Jute rugs that are trimmed in fabric (world market has them) and throw it down under the desk. It is kind of cute, can easily be cleaned and saves your current carpet:)

Good morning!

If you live near an IKEA, they sell an office chair mat for $19.99. We have had one in our office for over five years and its been great.

I would advise against the tarp or towel idea as they will get caught up in the chair wheels.

$40 is a good investment to protect your carpet. Mine cracked after 3 years so I built a pad out of 1/2" plywood, trim and a clearance box wood of laminate flooring - but I'm handier than the average husband.