I have a copy of Performance Products' catalog for the 123 series. For a new leather rear seat cover, it will cost $850. As for new carpeting, for the entire car, including the cargo area, you're looking at another $875. Now, I find P/Ps' prices to be high for just about everything, so I would look else where. You could try
www.wgautotop.com, www.4basic.com, or
www.hirschauto.com.
All 3 advertise in "The Star" as having upholstery and carpet sets. The ad for Hirsch list complete interior- rear seat covers in leather for $700.