Most of the stuff you listed is pretty easy and cheap to do yourself, it's just time consuming.
Door panel inserts (a pain to do but not difficult):-1-2 yards of vinyl from a fabric store: ~$30-3M vinyl top adhesive: $15 at Advance Auto (a lot more sticky than Super 77 or Super 90)-Screws or staples for a friends staple gun: $2 (some people say an electric staple gun doesn't work on the door panels, but my cheap Arrow TM50 works fine)
Be sure to do your glove box cover and replace the rotted stock speakers at the same time as the door panels.The 6.5" front speaker templates can be found here:
zerothread/183809Glove box recovering:
zerothread/212816
New molded carpet (again, a pain to do, but not difficult):-$90 + shipping at Rockauto.comInstall pics at
http://www.nissanperformancemag.com/august06/240/
1995-1998 240SX seats (you only have to remove/reinstall 5 nuts and one electrical connector for each seat):-$200 on a forum or at a junkyard
So, if you do it yourself, you're looking at less than $400 for new carpet, good seats, and redone door panel inserts and glove box. If you want to replace the speakers, I recommend Lightning Audio 6.5" 3-way speakers at Wal-Mart. They are rebranded Rockford Fosgates that cost $40/pair and sound almost as good as speakers that cost $120/pair.