I bought 1" Certainteed Ultra-Duct Gold. I ordered it from the company that installed the HVAC in my basement. They delivered it for $20/4x8 sheet. I used about 22 sheets. You could buy it for less but 22 sheets takes up a LOT of space and they carried in into my basement. This stuff was very similar to OC703. You can compare the specs between them here:http://www.bobgolds.com/AbsorptionCoefficients.htm
If you have an HVAC company that you use, give them a call to see what they have. I wanted to buy a couple more sheets from my guys and discovered that they only had some OC stuff that was not up to the Certainteed Ultra-Duct Gold and not anywhere near the OC 703. I guess they buy what they get the best deal on.