I couldn't agree with you more!  If you want simple, go to Smart and Final for plates, napkins, etc.  However, decorations are the issue for most locations.  Depending on your ideas and time, you can do picture boards, poster size blow ups of your parents and their early years, maybe kids and grandkids and their major milestones and accomplishments....that type of thing.  I helped to plan my aunt and uncle's 50th a few years ago and it was nice to have a picture of their wedding party framed on a mat that all of their guests had signed at the gathering.  As a reminder of the event, I also did a really nice album of pictures that I had copied from my grandma's phots...and then included their 50th anniversary photos as well.  With some time, I had it done in about 4 months - just in time for a Christmas present!  (I had ink pens that were photo safe and acid free to ensure they would be around for years to come).  My aunt loved it! 

If you need help blowing up an old photo that is in poor condition, go to Henley's downtown.  Most of all.....Enjoy it and don't worry about the decorations so much.  Your parents will appreciate the effort you have put forth...no matter what type of decorations you use.     

Another idea to use....You could decorate using colors and flowers that they used in their wedding.  For the western theme, you might be able to find cowboy boots, belt buckle, or hat at a second hand store to help with decorations.  I hope all goes well for the party.  I am sure it will be great and they will appreciate all the effort.  :)

Have you checked online??? There are a few party supply sites that have western theme party supplies... here are some of the sites i visit for party supplies:

http://www.shindigz.com/ind...

http://www.celebrateexpress...

www.orientaltrading.com

I used to work as in catering. There are so many things you can do! Think outside the box! Call around and get some hay bales, old boots ask on freecycle would look great maybe a saddle! All sorts of stuff comes to mind!