Get John Durie in:
http://www.heritageanddesign.co.uk/ to give you a survey.
Have a read of his website articles, they're quite illuminating.
I think you said it's an old stone built cottage? In which case you don't want chemical damp proofing but need an accurate assessment of why it's damp (i.e. non permeable render on walls, that sort of thing) and what solutions are available that are compatible with an old building which is meant to breathe.
Dunno how much you got off because of the damp but if you've got non breathable cement render or pointing it's not going to be cheap.....
