I think it's one of those things that is a 'selling the benifits' type of job.
My thing would be that as it's a show house, the standard has to be the highest and that will cost.
Me, from what you wrote, I would be thinking about the £200 to £250 mark for insides and out. £100 to £125 for the outsides.
They do expect to pay more for such work.
I can't give a time for one person but for us as there 3 of us, 3 hours maybe for insides and out. 2 hours for just the outsides.
I'd go for just the outsides and 'phone us' if they think the insides need doing.
It's also worth finding out if they are in a hurry to get the work done or if it has to be done on an exact date. If they are, then up the price.
Cheers