Matt, as they are using the existing wiring i think that a bit expensive. I have 3 PIR's, remote key pad, 4 screamers front and back door sensors. In the garage i have 2 additional PIR's and 3 door switches all wired through the tamper circuit in the house alarm and also wired into a seperate garage alarm and all the materials cost me £175. In additional to that i bought a 4 camera wireless camera kit for £80 off ebay from hong kong. The kit consists of 4 camera and a control box which plugs into my HD recorder, its really good for the money. The cameras cover front, side and rear of the house and inside the garage also.
One thing to remember if you get a camera make sure you display signs telling anyone coming on to you property you have cameras. I got in hot water with the old bill and was cautioned for not having signs..... Yes i no it stupid but its the law apperenty