Hi Jonathan,
The glow plugs issue does sound a bit like a problem with the fuel system that could well be a cheap fix - a can of Diesel Magic or any other brand of fuel system cleaner could make a big difference.
The electrical problem could be down to the battery being on the way out, and it would be worth getting it tested.
Let us know how you get on --- I would be inclined to keep your wallet deep in your pocket until the garage does something to cure the problem.
Regards,
Peter.