These weekly races are still pretty cheap at NYRR and the new series is just for the dedicated with the no frills. However, the NYC half and the marathon are out of control expensive.
For truly cheap, no frills races with some decent competition, run the Lake Merced series in San Francisco. Beautiful setting, bike path around the lake, some small hills, and something like a $1 fee because the city charges that for parking, and they usually bring tasty brownies or cookies or the like, for free.