As with the review from the undertaker I believe a lot of undertakers DON'T use the pre-paid system because, when the inevitable happens, they can make more money by preying on the grieving vulnerable relatives at the time.
I have said before how can a funeral home justify asking say two and a half grand for a burial/cremation {and that's the cheaper end} when if you break down the costs to the undertaker it doesn't come near that amount. I realise they are businesses after all and I'm all for businesses making a profit, but there's profit and an out and out rip off, and funeral homes tread that fine line, and lets face it they will NEVER be struggling for business, death is an inevitability .
If you break down say a basic cremation... the undertaker will keep your loved one for about a week, put them in a coffin, transport them to the Crem with perhaps another car for the immediate family, pallbearers will take in the coffin then after the service will run the family either back home or to the wake total time from start to finish 3 hours tops.
The body is kept for a week it's not costing anything, the coffin purchased by the family {if cremation} will no doubt be used again, a couple of vehicles used for a couple of hours and pallbearers {only employed on a ad hoc basis}
If you did {or was allowed to do} a D.I.Y. funeral yourself the above you would need to do I estimate would probably cost you in the region of £600 to £800.
I remember as a boy the only time we saw "flashy" motors on the street was a funeral cortege and as very few people drove or owned motor cars in those days some funerals could have upwards of 3 or 4 cars following the hearse, I bet it wasn't cheap then so just imagine the cost of that now.