High-quality, affordable bike tour group in the US?

There is a company based in Oakland called Backroads--you can google them--they offer really great trips but they are very pricey. For a chaper option, this is kind of a wacky recommendation, but I've heard of this group called the biking superheroes. They are volunteers who bike across the U.S. and stop in cities along the way where they just walk into city hall and ask what needs to be done--then they spontaneously volunteer and build trails, paint low-income houses, whatever--and then bike to the next city. They wear superhero capes while they bike. There's no guide but it's free to join up with them. It's all people in their 20s and 30s. You can check out more here: http://www.sierraclub.org/sierra/200607/one_small_step.asp

melanie works with the transportation and land use coalition in oakland now - if you want to ask her about superhero rides

btw, here is another group that I recently came across that offers inexpensive "bike-volunteer" trips: http://www.democracybike.com/index.shtml