Some things never really change, while the Core 2 Duo series has been a force to reckon with since day one, the Celeron series is still pretty much the same. While the Celeron 420 processor is very cheap at just $50 US there are still much better options available at this price. The Celeron 440 was very slow at 2.4GHz so imagine one of these processors clocked at just 1.6GHz. The Athlon64 X2 3600+ processor can be had for just $60 US and if you are planning on building an ultra cheap system this is the path we would choose.
Check it out at Legion Hardware.