I suggest you approach the task of "restoring" your future Mustang methodically.
First, keep in mind that the word "restoration" has no single standardized meaning. For example, some folks will buy a can of Ford Blue spray paint and paint their old worn out engine so it is shiny. I call this a "Rattle Can Restoration" Likewise, when someone represents their car as having a frame off restoration, they clearly do not understand Mustangs. Mustangs are not body on frame construction so no "frame off" is possible. Some sellers describe their cars as "Show winning", to which I would ask, which MCA Grand National shows have you won with that car? In all probability, none. LOL
Second, this brings us to the notion of goals and paths. What exactly do you want the car to be when it is done? (a beater, a daily driver, a restomod, a cruiser, a track car, a concours winning trailered show car, or what?) Having a clear sense of the goal and a plan to get there gives you a direction and a target.
Third, to put your enthusiasm into perspective, shop the market for a car that is already "done" to your level of acceptable quality and essentially turn key ready to enjoy for the purpose(s) you intend to use it. What would the amount on the check need to be to bring that "done" car home? In theory, that should be the total cost of restoration including the car itself.
Fourth, to determine the restoration part of your budget, look at available project cars that you might ultimately select to "restore". The purchase price of the project car then needs to be subtracted from the "done" car total price from the paragraph above. In theory, again, that should be your "restoration" budget.
Fifth, in practice throw "theory" out the window. With project creep the total "done" cost can climb significantly. Many done cars cost their owners more than they are worth and the seller is taking a loss on the restoration. For many hobbyists, being upside down on a car is an unpleasant reality. For others it is unacceptable. You have to decide where you fall on that spectrum.
Sixth, a search of this forum will uncover similar threads where attempts have been made to quantify the total cost of a "restoration". Those threads often include a "formula" that goes something like this: Add up all the parts, all the labor at your local hourly rates , all the upgrades and multiply that number by at least 2.5 to get to your actual cost.
Seventh: the key take away is be patient, attend car shows and talk to owners who have already been down the "restoration" road, sort of a "walk a mile in their shoes" exercise to see if your wallet and your other resources are up for the task. Reread "Third" above.
Good luck and welcome.
