Hi Leclerc,
I think you are running 6 volts which will limit your choices a bit.
I was looking at a Light 15 the other day which has an SU pump – not sure which one but they seem to be about £80.
Examples here:
http://www.holden.co.uk/displayProducts.asp?sg=2&pgCode=015&sgName=Hardware&pgName=Fuel+Pumps&agCode=0100&agName=SU+Fuel+Pumps
On the other hand Chris offers repair kits for the mechanical pump for £10 – 20 depending on what you have. A mechanical pump in good nick should do the job and the repair kit covers the parts that fail.
Chris