The price seems very reasonable, but check if this price includes all,, scaffolding, materials, + VAT if applicable,, and is the work gauranteed. It's always handy to get it in writing too if you can. Get someone who knows what they are looking at, to give their opinion on the quality of the finished work being carried out locally. If you do decide to go ahead, tell/show the "roughcasters" the bossed/bad areas of roughcast that need replacing,,,, ask if the window and door reveals will be re-rendered too,,,,, let them think you know what you're talking about, and what you're looking for..... When the job goes ahead, they should cut out all the bossed/loose areas of r/cast, treat and then scratch coat those areas back out to the original level. The patching s/coat would be done the day before and allowed to set... Next day, or so,, the walls would then be roughcasted over the original... This is a very sound and popular way to roughcast, and will give your house a brand new look,,, but go and ask a neighbour or two if they have any complaints with their finished job,, and are they happy with the overall result,,, because you're thinking of getting yours done too...... You could also get a couple of quotes from local roughcasting contractors, just to compare all the prices,,,, you can't be too careful.
Roughcaster.