Front Discs = £35
Front pads see above
Front brake lines =£20
Oil filter = £8
Air filter = £6
Fuel filter =£8
Oil = £20
battery =£40
Rear cross member = Has to be fabricated so cost could be huge
rear arches £31.20 (for both) + VAT
side panel £10.80 + VAT
front arches £17.50 each + VAT
roll cage ??? what part as there isn't a roll cage in a Transit or do you mean the front rollbar? If so no idea if you don't have one then you can't fit one without changing the wishbones (I think it is that part either way you need the fixing points), my first MK3 didn't have one (rollbar) but the next one did and there was only 18 months between the two.
play in the steering =Exchange rack approx £100
battery tray = £17.90 inc bracket = VAT
rear right wheel bearings = £20ish
spare wheel =£5 - £20 (breakers)
front wing =£26.55 + VAT
back doors = how much do you want to spend as lots on ebay
All the +VAT Prices are from Beevers (sponsors of the Members progress reports) and there will be delivery on top as well the rest of the parts you can get from any decent motor factors some of the prices are 'ish in that give or take a couple of pounds either way. The brake discs and pads can be bought on ebay complete from several sellers so that is an average price for 14" wheel.
You are well under a grand parts wise BUT you now have to add in the cost for someone to do it for you, then there is painting on top, average quick blow over is £300 up to silly figures.
The above is just shy of £400 without any VAT not including the rear crosspiece, not including delivery and no labour costs nor the paint afterwards. That is, if the list is a definitive list, remember you still have to add in the sills and the shocker tops.
You could of course bite the bullet and take anything good off the van...maybe around £100 - £200 tops on ebay (if you can find the buyers)and scrap the van for approx £65-100 (depending on what junk you could put in the back

) and then you will be more or less back to square one.