I made a fair few mistakes along the way which I'll share now.
1. The eBay windscreen wire is OK but I went through that very fast and found something better in B&Q at 58p/metre. It's their thinnest cut-to-length cable and you unwind the wire bundles (there are about 6 in the cable) to get the right thickness. 3 metres is more than enough to do 2 screens (because you're really getting 18 metres once unwound).
2. The trim that surrounds the screen is plastic coated Aluminium. It has a rubber seal on the outside.
I cut away the rubber seal with a stanley knife. At first I went through the Aluminium and plastic and that broke the wire often and splintered little shards off the edge of the glass. Then I found a way to go under the trim, by pulling the wire in the direction of the gap between the windscreen and the body. Cutting away the rubber seal helped to get under the trim.
3. At one point I was about half way round and had the thought that if I lifted the glass a little the wire would go through more easily. The glass cracked so I won't be trying that again.
4. I made the pilot hole for the wire with a hot soldering iron tip in one of the bottom RH corners. The sealant is at its thickest there.
5. The wire moves fastest when it's hottest which is really frustrating as you start to see the smoke coming just as you have to stop due to physical exhaustion.
6. There's a technique for getting round the upper corners that worked where you wind the wire around the ocrner and tuck it under the seal when about 3cm off.
Once I had the right technique it was quick and easy. Getting the broken one off has been a useful preparation.
It's taken about 4 hours but I think under 1.5 hours will be possible next time.
Cost wise I think the best deal I could get for a new screen was £145 + £20 trim + VAT
(About £200, most quotes were around £250)
That compares with about £1.70 for wire, £20 for a S/H screen, and £10.50 for the sealant/primer kit. (About £35 in total)
Windscreen cover would've been better.