Cheapest digital SLR camera?
Cheap digital SLR camera in nikon, canon & sony?
Why go cheap? Have no idea why anyone would go that Route if you want to take a good photograph.
The cheapest DSLR (new) I know of is the Sony A290. The Olympus E-450 and Pentax K-x were cheap too but I don't know if they're still available new.
After that look at the Pentax K-r, Canon 1100D and Nikon D3100.
Probably the used route.
Cheapest are Canon EOS XS, T3, Nikon D3100 and Sony A390. Skip Sony's older models though.
Here's a DSLR Buying Guide - http://www.the-dslr-photographer.com/2009/11/which-dslr-to-buy/