Erick, welcome aboard.

A quick answer to your three part question is: Body = $5,000-$10,000 , Chassis = $5,000-$10,000 , Interior = $1,000 - $15,000 . As Dave points out, it all depends on what you value, and what style you choose. You mentioned a coupe body, so you have two style choices with variants within. There is the three window coupe, and the 5 window coupe. They are available in stock heighth, or chopped, and the amount of chop can vary from any of several manufacturers. As far as where each manufacturer is located, that's probably not too important as many have dealers located in your area. Or they will sell you directly, either way, shipping is involved, you either pay it yourself, or pay the dealer. Sometimes you can save a bit on shipping by purchasing from a dealer who may be out of your area, but who is coming to a major rod event (either NSRA or Goodguys) in your area to have a display. Since they will use the body as part of their event display, they often will not charge you the transport cost.

I suspect you've been doing the Mustang thing for a long time, and have accumulated considerable knowledge over time. It's not any different with the rod stuff. Sure, we can help you with some of the particulars, but you really need to do some personal observation and determine a style that presses your buttons. Nothing becomes more frustrating, and costly, than to start a project down one path, only to be influenced later into changing directions. It's getting late in the season now to go to shows and "kick some tires", but that's usually the best place to start. That way you can observe the approaches utilized by others to achieve an objective that appeals to you. I don't know if your primary approach to cars so far has been restoration, or modification. With restoration, the "blueprint" is predetermined by the original manufacturer, and all the restorer need do is follow the original plan. (Not to make light of the dedication to originality, and pitfalls of parts location, and skill of execution necessary). But with hot rods there's an extra step(s) of style planning. The options for execution are endless, and therefore require more planning than even the most demanding restoration. This is not intended as discouragement, but rather information to make the journey more enjoyable, and ultimately more successful. As you become more familiar with rods you come to observe there are pleasing results, and, unfortunately, less pleasing ones, often utilizing many of the same components. It's largely about execution, and only partially about componentry.