HI. I have been involved in the building trade since the 1980's so I reckon I can answer this for you.! You would need to consider 2 different types of coatings. I have posted the links to what i think is the info you need.
Option one: Have the wall repaired (such as bad bricks and loose pointing) and have a clear coating applied like on this page
http://www.neverpaint...ure-penetrating-damp/
Quite reasonably priced too. We had it done a while ago. It doesn't leave a nasty shine on the bricks either.
Other option is coloured wall coatings like this
http://www.neverpaint....co.uk/wall-coatings/ a bit pricier but lasts for years, my uncle had his done 10 years ago (dont know what company though) and it still looks good, but i cant remember if he had damp or not?
Price wise not sure, best to contact a few firms like this and ask. hope that helps you.