I was recently considering buying a house with storage heaters and like you also wondered how much it would cost to put gas central heating in.
I found you can get an estimate for the installation of the gas supply pipework and meter by going to the Wales and West Utilities website and filling in their online form. Within a couple of weeks the estimate came through the post.
Sounds like your gas pipe is a lot nearer to the property than the one I was looking at. Wales and West Utilities quoted £676.80 to supply a meter box on side of house and connect to gas main out on main road. This was for a 2 man team to dig up and lay 20 metres of pipework on public highway and 5 metres on private land of the property. Hope this helps.