Well, I ended up picking up an umbrella set from Amazon, which wasn't a bad deal - $40 or so for three umbrellas, a mount, and a free mic stand. I already had a manfrotto umbrella mount, so two of us could use these on our stands. We ran our regular gear with the umbrellas. It poured at one point during the show, for about 25min. The rain was coming straight down, and the umbrellas worked perfectly. Mics were nice and dry, no baggies necessary. If it had been that nasty kind of more horizontal rain, we'd probably have had to pull down, but as it was, it worked out OK.
I can find the link to this set if ppl are interested. These umbrellas are for camera lights, and are a bit bigger than the umbrellas Ted used to sell. The mount that came with them was nice and easy to use, too.