There is no set price for a LGSR, I charge a set rate for the 1st appliance, then an additional price for every appliance there after!
You may want to discount if a LL has lots of property's, and lots of ongoing work!
If you see flames while driving- get out quick!!, lol
You should be fine! an old Vivaro of mine did the same when the MAF sensor went, she drove exactly the same for a couple of hundred miles before the mechanic fixed it
This lead should be in the LH terminal on the genny, early cds had a separate earth in the RH terminal on the genny, have you checked the electrodes inside combustion chamber?, pcb sounds ok at the mo,