I’ve recently gotten in touch with Chris Fries in Chicago through the Balloon_Sked mailing list for amateur near space balloon missions. He’s not going to near space but what his setup is elegant, simple, and very low weight. He attaches a <3oz payload to some standard aluminized mylar party balloons, and his balloons blog for themselves reporting location, images, and video through PCS-band GSM/UMTS cellphone signals. I hope he posts a how-to on his setup. Launches here here and here.