mpg question, 5lug access cab 4 cylinder

Hi folks !!!!
So I'm buying a 2nd car for family and mpg use.

So decided on a 4 cylinder regular or access cab automatic
Transmission. 06-09 model tacoma.

Price range is under 15k. And found quite a few.with under 45,000
Miles on them.

One stood out, access cab, silver, 4 cylinder, automatic
With paint match camper shell.40,000 mile For 14,000$

I plan throw on some all terrains, either 215 or 235.
No lift

how much of the mpg will be affected?
Camp shell + 215 or 230 all terrains.

stock mpg being 19-25