I wouldn't like to say which model is more suited for digiscoping, I've only ever digiscoped with a Sony W5 compact. It looks like Don's research has found a potential fly in the ointment for the D40, but he raises some very valid points regarding the expected quality of the results.
If you do decide to go Pentax, then these people do the K100D cheap:
http://www.cameraworld.co.uk/ViewPro...SUBCAT_CODE=51
They did have some refurbished ones with manufacturer's guarantee for £249, which is a bit of a bargain by anyone's standard.
Having digiscoped with both a cheap (non-ED glass) 'scope, and a better quality item (Kowa 663), I would say that it's well, well worth getting a better scope. Your "keeper" rate will be miniscule with a non-ED glass scope, regardless of the camera you hang on the back of it.
Hope this helps.
Duncan