Setup a reliable home Wifi network in a large house

We need a freelancer who has good experience of setting up WiFi networks in large houses where a normal Wifi Signal is not strong enough to reach all areas.
The houes has 5 computers, two PS3\'s an Ipad, Mobile phones and wireless printers dotted around and all of these need to be setup in a reliable network.
Home networking is not an area that we specialise in but as this job is for the MD of one or our main customers we need to stop \"tinkering\" with this and get the job done properly. The site has just had a new 50Mb Virgin internet connection installed and thus we now need to make sure that the wireless network is setup correctly.
We have tried a number of different routers and ethernet over power wireless extenders but things just seem to go wrong and end up with us going backwards and forwards to deal with the issues.
We have reached the stage where our only way fowards would be to run Ethernet throughout the house but the property is finished to such a high standard that the idea of drilling holes in the walls does not appeal to anybody.
If there is someone out there that feels confident that they can implement a realiable solution along with a set of simple end user instructions for very basic trouble shooting (e.g. power this box of and on again should this happen etc.) then we would be happy to hand this job over or pay for consultancy and ues our own engineers to implement the recommendations.