Thanks to Stephanie, I found this info:

Item No. Postage Value Price Per Sheet 1 -1 2 -9 10 -99 100 +
Postcard $0.26 15.99 13.99 11.99 Contact Us
1st Class Letter 1oz $0.41 18.99 16.99 14.99
Square/Odd-Shaped 1 oz. Letters $0.58 22.99 20.99 18.99
1st Class Letter 2oz $0.58 22.99 20.99 18.99
1st Class Letter 3oz $0.75 26.99 24.99 22.99
1st Class Letter 3.5oz $0.92 30.99 28.99 26.99
1st Class 4oz $1.31 38.99 36.99 34.99
Priority Mail - 1lb Flat Rate Env. $4.60 109.99 107.99 105.99

I e-mailed asking for a price quote for 1000 and requesting a charity discount. Hopefully this will be cheap enough that we can order them in bulk.

In the meantime, if any of you want to use one of our logo graphics and order them yourself from stamps.com, please feel free to do so!