The difference in my own expenses is fairly significant.
Metered water bill, renting a small storage unit where water is filtered/items stored (a small rented garage was sufficient previously but it has no water or electric), much higher vehicle running costs due to using a much bigger payload van and insuring as a modified vehicle (not to mention the extra diesel required to lug weight around), Water filtering kit, much more expensive tool replacements.
Take them one at a time with estimations or annual averages if needed
1)WFP Metered water £350 p.a. , Trad £0 as taken from unmetered domestic supply.
2) WFP rent £1,650 p.a. , Trad c. £500 p.a. (with less for it though)
3) WFP vehicle running fuel £2.2k , insurance £500, repairs/servicing £1k
Trad fuel £1.5k , insurance £300 , repairs servicing £400
4) WFP Water filtering items (RO, DI, pre filters) £250 p.a. Trad £0
WFP other tools/items such as poles, microfibres/scrim, connectors, upgrades backpack and misc. I will have a stab at £300 a year though it's hard to average. - Trad maybe £70 a year if including replacing a ladder every few years.
So I've got £6,250 for WFP and £2,770 for trad - a difference of £3,480. However, my situation is exacerbated by WFP forcing me to rent a small unit. With trad, although I rented a garage, I could have dispensed with that if pushed. If I had been able to filter water at home, I would have saved £1,650 - so the difference would have been more like £1,800.
Also, my figures above make no real provision for some of the *initial* outlay. Obviously total accuracy is nigh on impossible as things fluctuate year to year. Additionally, although my outgoings are est. £3,480 higher, my extra turnover from WFP over trad dwarfs that figure.
Anyway, I think it's fairer to go with the £1,800 p a difference as most guys will filter water from home.