Alright @anon810895, I calculate that over a 30 year period, assuming annual returns of 8%, you would save £2,466.92 by manually replicating the Vanguard Lifestrategy 80% fund.
I just calculated the difference in cost for a max’ed out ISA, which is £20 on a £20k annual contribution (£20,000 * (0.22% - 0.12%). Then compound this money that you’ve saved at a rate of 8% annually, adding the saving amount every year:
Edit: Your actual ISA would return exactly 1000 x that, obviously: £2,466,917.36