Bricks, Masonry, Asphalt and Concrete - Foundation for new shed

I'm thinking about building a shed in my backyard. I'm looking at 12'x16' stick frame. The soil is pretty firm. The homes in this area are about 45 years old and foundation problems are nearly unheard of.
I've had 4 estimates for a slab. All included 12" wide x 16" deep footings with #4 top and bottom horizontal steel, #3 stirrups and #3 slab steel at 24" each way. There would be one interior beam across the 12' section.
One of my neighbors has a similar size shed built several years ago and he told me the footing sizes I have seem like more than I need.
Since this is just a storage shed, I don't want to hire a PE to check this out.
Does this foundation seem reasonable? Also, the estimates I have vary quite a bit. Living in South Texas, is there a way I can determine what price is reasonable? If this is going to be that much trouble, I'm thinking I might just pour some piers myself and use a wood floor, but I really hate to go that route.
Thank for any help.

I think it is overkill!
I had a 12x10 slab poured on DFW Texas clay 10yrs ago,no problems.
Minimum prep was done,2x4 framing ,rolled wire mesh ,no interior beams.
I placed a Home Depot kit shed on it,fixin' to replace soon with a metal shed.

If your handy,frame it yourself and you can get pre-mixed concrete in a towable
unit from U-haul or some rental yards.
You can beef things up if you want with deeper perimeter beams,rebar etc...

Your building permit office might be able to help with this, by advising what might be required with this size slab. It may also be able to help with the permit, if one is needed. In any event, the information should be helpful. What you have listed does seem to be overkill.

I appreciate the input. The more I thought on this, the more wrong it seemed. I'll contact the local permit office and see if they can offer any help. I do know there are no foundation requirements and no permit is necessary for a structure 200 sf or less.