How much should I budget for TV install?

[Easty-5]

We have bought a new build house that will be ready April 2015. I am starting to work out how much we need to budget for everything and I have a price for everything other than our TV installation. I will be looking for the following;

1. A 50-55" TV mounted on our living room wall with Sky+HD & soundbar. We would also maybe like a socket with HDMI connections down near the bottom corner of the wall for temporary connections.
2. A ~32" TV mounted on our bedroom wall with Sky+HD Multiroom.
3. A ~40" TV Mounted on the wall in Bedroom 3 with a Sky Magic eye or the equivalent. A socket with HDMi connects near the bottom of the wall so I can connect my XBox One.

I will be having additional sky points put in the rooms and a double socket in the middle of each wall. Is there anything else I can have the developer do to make life easier for the guys installing my TVs. Running the HDMi cables behind the wall is out of the question. They wanted £605 per room to run 3 cables!

Also, does anybody have a rough estimate at how much I should look at budgeting for just the installation, not the cost of TVs & Soundbar? I am in North East Scotland if that makes any difference.