www.specialtybottle.com and www.jarstore.com have some good deals. If you're not going to actually use them for canning, you don't need to get the ones with two-part lids. Otherwise, if you just want Ball jars, your local grocery store, Target or Walmart will have them.
You can also go to the Wedding Classifieds board or look on craigslist. Rustic weddings has got to be the number one theme in the last few years and I guarantee people are reselling these.
Re: Mason Jars