Thanks all, and yes the moneypit seems to be wanting more of my money. I'm determined to get this car MOTd and back on the road, and I can't wait for that day! Long road ahead.
Luckily my brother almost single-handedly re-built a Fiat Uno turbo years ago, that thing was more welds than bodywork in the end, so he's got the MIG welder and the practice so I think he'll be getting called upon.
I'd found the Skandix parts, so I was thinking about:
http://www.skandix.de/en/spare-parts/bo ... t/1046616/
and the right one, hopefully I can then weld these into place and should recover them.
For the wheel arches, I'm unsure. I might be able to do small patches to recover these, so will tackle those separately and hopefully won't need the full wheel arch replacements.
Not ideal, but I'm not going to let this beat me, will document and make photos as I go along, but any advice or adding other supplies/sources for the sills or parts please let me know.