If damp is showing up internally, then I would investigate that thoroughly before committing to re-rendering.
Most internal "damp patches" are usually not rising, but as a result of condensation, lack of good regular heating, ventilation, lack of extractor fans, breathing etc ;o)
Do have someone advise before going for re-render.
I would allow 5-6 thousand to include scaffolding, rubbish disposal, and VAT.