Is $10,400 a reasonable price for a 2006 Mustang?

$10,700 is full retail price according to edmunds.com so it looks like the dealer is slowly getting the car closer to a reasonable price. But realize this, NOBODY pays full retail for a used car. Everyone wants a bargain. The wholesale price of this car is only $8700 so you should be looking to pay somewhere between retail and wholesale for the car. If you are serious I would offer them $9500 and not a dime more.

Nope, still asking too much. The car has been sitting on the lot for several months for good reason. It has been abused. Mods actually decrease the value of an automobile, not increase it. Avoid this purchase.

It sounds like a pretty good deal, but before I go with it I would bring a MECANIC to check it under the hood. 78 000 miles is also a bit much for a 5 year old car, but again, if everything is good under the hood, you should be fine. Mods do bring down value, so you might be able to negociate the price a bit more. I would also watch out for engine mods. Bringing a mecanic or any other car expert that knows their stuff to check it out and even test drive it would be your best bet. You can also ask for the carfax to see all accidents that the car has been in and more info about its servicing. Overall to me it sounds like a great car. Mustangs are known to be sturdy and reliable, but checking what I listed above will determine if the engine is good. Good luck and I really hope everything checks out so you can enjoy the mustang experience!!

Sure. Look at others for sale with similar features: https://usedcars.truecar.com/cars/used-for-sale-Ford.Mustang/location-10075/year-2006.2006