My rendering on the back 2 walls of my 2 bed mid terrace house is cracking badly. It is approx. 30 years since rendering was completed in a poor fashion by previous owner. This problem is causing plaster to come off in bathroom, blackening of paintwork in kitchen and a feeling of dampness in upper back bedroom and lower back room. I do need a new damp course, but I know the rendering state of the rendering is not helping. My roof is sound I have been reliably informed. How much would a job like this normally cost from?