Having just done an interior restoration on our 97 (97 and 2000 interiors are virtually identical), I can hopefully help a little here...A quality paint job on a mustang can easily run up to 5-7 thousand dollars. That would include door jambs, etc...I do know of someone who Maaco'd their old pickup for 500 bucks, but it was a terrible paint job. On the door panels, if you can provide a pic of the door clip that's broken, that would help as Im not sure what you're referring to. If it's what I think it is, those are fixed with about 4 dollars

. A convertible top itself ranges about 2-300 dollars. Installation is where most people get burned bad. Don't bother with Ford as they charge several thousand to replace a vert. Find an upholstery shop that has done them and ask to either see pics of the work or a customer reference. If you are referring to floor mats when you say rugs or the carpet itself. Floor mats are the ones you take out and can clean the carpet underneath. Mats run anywhere from 10/15 up into the 100's depending on make and quality. For a good cool looking one, expect 75-100 for a full set. The carpet itself in the interior is surprisingly very cheap. About 125-150 dollars. But the install...it can take quite a bit of elbow grease. However, almost nothing refreshes the interior like new carpet. The other wild card here financially is your drivers seat. I wouldnt recommend an after market seat as there is a lot of hidden costs like mounting rails, etc... If you're looking to go cheap, there are some pretty nice seat covers you can install yourself in 15-30 minutes and run maybe 50-100 dollars. If you want it reupholstered, that can range from 200 for vinyl to 500 or more for leather.
The advantage is that all of this can be done over time too. If you plan on moving forward with a project like this, I'd recommend that the first thing you have done it the paint if you would consider doing any of it yourself. It will likely be the most expensive and take the most time if it's done with quality. Make sure you shop around for the best work and the best price. The caveat is that if that's done first, naturally be careful when moving things out of the interior so you don't scratch your new paint, but the cool part is with a vert, it's really easy to do interior work. I know...I'm 6'2"! I say paint first because if they overspray like the top, now you've got paint on your new top! You could have the paint shop probably replace the convertible top too now that I'm thinking about it.
Remember you can spread this out over time too. You don't need to do it all at once. Convertibles of virtually every make and model tend to hold their value much better than a coupe, but they have to be in good condition. If your convertible top is in need of replacing, it's likely you'll take a big loss at trade in time. You'd be better off selling probably to a private party than a trade.