My Auster has the ever efficient Armstrong starter and a brace of gell cell motorbike batteries in a nice wooden box to power the radio. I'm with tacpot on recommending this as a cheap and simple solution to lack of lectricity.
To convert a C-85-8 to lecky start is going to cost you at least 1,000 of your British pounds plus loads of hassle sourcing bits. Unless your pal really loves the Chief I would recommend selling it and buying an aeroplane with a self commencer already fitted.