You can buy a complete black interior without carpet or seats for 2-300 dollars from what I've seen. I have no experience dying
I just put new carpeting into my mustang, and what a world of difference it makes to the interior. Everything looks brand new now. The installation itself was not very difficult, just annoying getting everything fit back in. Make sure that you make every cut very carefully (seat belts, center console) so you don't have to explain to your friends why there is a bunch of holes in your brand new carpet. The install is just basically cut and fit. I got my carpet from ACC, and it fit in perfectly. The carpet sits higher (it's new), so it can be a pain trying to fit the center console and some of the side paneling back on