My sew-it-yourself interior
There are a few pictures of the interior I sewed for my 6A at this website...
http://www.eaa582.org/gallery/thumbnails.php?album=19&page=1
I bought the foam from Van's and the fabric from a local auto upholstery supply store. They let me take the fabric sample books home so my wife could help with the color & texture decisions. The fabric cost ~$200 and at the time Van's foam was also about $200.
I also sewed seat heater elements ($70 for both seats) between the blue fabric and a 1/2" foam filler-layer that went over Van's foam. I love my heated seats the most after preflighting in single digit temps, while I wait for the engine to warm up!
The side panels are made of corrugated plastic sign-board with a single layer of thin batting material and the color fabric wrapped around and glued on with 3M #77 spray adhesive. Real quick and simple. Most are just friction fit into the plane, 1 or 2 have a small piece of Velcro on the back.
The armrests took a little trial & error. After the seats were done I sat in the cockpit making airplane noises. I decided I wanted to be able to rest my elbow on the armrest without leaning over, that required a layer of 2" (firm) foam. I mounted the foam to a piece of 3/8 plywood so I could staple the fabric cover on, and I mounted the armrest pad to the airplane with short wood screws, the ONLY wood screws in my all-metal airplane! The wood also adds a bunch of much-needed stiffness to the armrest.
It took me about 6 weeks to make everything (nights & weekends). If you have more time than money (like me) then I think it's worth it. I never did any kind of upholstery before I started on this, but then again, I never built an airplane either! It was a great learning experience, the next time will be much easier.
I don't know how much complete interiors are going for, but I have less than $500 + labor in my very custom interior. It also gave me an opportunity to teach my (then) 9 year old daughter how to use the sewing machine. This and the pride in knowing I did it myself = Priceless! I say go for it!