Replacing the rims yourself will save you some cash on new rims. It’s a pretty easy DIY, but if you don’t feel comfortable handling it yourself, a mechanic is likely to charge you around $50 per wheel in labor.
Mustangs rims are typically 8 inches wide and 18 inches in diameter, for all ‘stangs with model years after 2006. 9 inch and 10 inch wide rims can also fit on a Mustang, but only on the rear two wheels.