I bit the bullet and bought a Tubus Cargo for my touring bike and don't regret it. You can buy Tubus racks much cheaper on-line from British shops such as Wiggle or Probikekit, often with free shipping. I also have some cheaper racks, but here are the Tubus advantages:

-- Very strong and well made with high weight loads.
-- Relatively light weight, particularly considering the strength.
-- Designed with adaptability to fit just about any frame.
-- Fit Ortlieb panniers perfectly, which are also topnotch.

That said, I recently bought a Planet Bike Koko rack for commuting, and it is an excellent value for the money (about $30). It won't hold as much weight as the Tubus and is heavier, but a very solid rack for the money. For loaded touring, however, I would spend the extra money on a Tubus.