I googled how much it would cost me to install a garage, and it turns
out to be starting at $7K for a 1 car garage. So, will I win $2K at
the time of resale ?
That assumes that you can install it for $7,000. If the property with the smaller garage is not big enough, the local government will not allow you to add width to the garage. You and any future owner will be locked in forever.
The first question for you is will you get the use out of it. If the answer is yes, then it probably makes sense.
The resale value issue is: does my choice make my house a better option for a typical resident of this area. Or does my choice limit the ability to sell.
If the choice is a one car garage, but you insist the builder build a 7 car garage. Then you limit the set of potential buyers to those who desire extra-extra large garages. But the reverse is also true. You don't want the cheapest by far.
Look at the other houses that have been built. Have the majority been one option or the other, or are they evenly split. If the split is not heavily biased toward one option the difference in ability to sell is negligible.