I would hit the local salvage yards. the ones that you have to go in and pull the parts yourself will be the cheapest, and it doesn't even take tools to remove the tailgate. You might get lucky and find a green tailgate and not have to paint it.
seats may be harder to find, but the junkyard/ salvage yard is a good start. you might even be able to get the seat covers and foam from LMC truck and reupholster your originals. You can also get the tailgate from LMC, but it will not be as heavy or as good of quality.
Another nice thing is that a tailgate from a 1993 all the way up to 2012 Ranger will fit your truck, so you have lots of choices
before scrapping your old tailgate, remove the mechanicals from it (handle, hinges, linkage etc...) could come in handy later.
Btw, welcome to TRS, take your time and browse through the site. Check out the "Tech Articles" link, and that will give you a wealth of knowledge on common issues and how to fix them. Do a brows through the the subforums for interior, and there is a good possibility that there are several threads on how to reupholster your existing seats, or a least it will give you an idea of how to remove them easily.
AJ