I tend to base my price for a job on an hourly/half daily/full daily rate plus the price of materials with mark up. If i think a job is going to take me two hours, the estimate I send to the customer will show the full cost of two hours labour and the cost of materials seperately and then a combined total.
I find that pricing per point is too broad. Lets say for example that two different customers want one socket installed each. One wants a socket installed, surface mounted right next to an exsisting surface mounted socket and they already have RCD protection and bonding in place. The other however has an old rewireable fusebox (no RCD protection, with no gas or water bonding and they want a new socket installing, sank in/flush mounted in tiles above their kitchen worktop with the cable chased in and run under the floor to the fusebox 10 meters away on the other side of the house. I can't believe that anyone would charge per point given these two scenarios.