Think you are right how long is piece of string.We paid 22k for 04 plate Eldiss Sunseeker on the road.It had 11 thousand on the clock 4 years later it has 43k on clock,would say we have done 20k of that abroad.Tax, insurance,comes to £500 a year,service probably another £400 including Habitation check
using mobile service.Last year we spent 15 weeks away in van,this about 12 weeks.We work on assumption that while we are away we don't use gas at home,on water meter so no water used ,less electric freezer is left on.Food you have to eat some where ,as long as you don't eat out every night you are away cost the same.No fuel in the car.
When I was working we always went to Greece twice a year for two weeks at a time ,Flight and apartment for two weeks was between £800 and a thousand pounds,we ate all meals out another thousand so we are looking at nearly 2k. This year we had one trip of 6 weeks away,went through Belgium,France,into Spain,then down as far as Cordoba for patio flower festival.Back via the Pyrenees,Monet s gardens. in France.Saw wonderful buildings ,gardens ,flowers meet great people.Total mileage 3500 cost £2200.Earlier in year we had two weeks in Goa well over £2k spent, bored with sitting on beach after 8 days.
My advice before you buy,hire make sure its what you want to do,we had 6 weeks in MH in New Zealand before we brought.
But we still go back to how long is a piece of string,as expensive or as cheap as you want to make it or use it.

When we first started we did the real budget thing I cant remember the figures now but by going for long enough proved at the time that you can live cheaper in the van than at home.

To achieve this you must spend time at your locations, you must be prepared to not stay in campsites or just occasionally when you need launderette services for example, you must be prepared to cook 'at home'. Most people save by not storing up the cupboards as you can only buy what you have space for.

You get to see things and places that you never would on a package holiday. As the other poster said you save on your home bills. Apart from the initial outlay I am not saying it will always be cheaper because that depends upon how you travel but it can be and IMHO you will get a lot more for your cash in your MH

So its true 'how long is a piece of string' a lot depends on how you want to travel.

Here's a good alternative question.........what does it cost NOT to go motorhoming.
Think about it.

We get withdrawal symptoms if we've not been on tour in our MH after a couple of months.
The places we wouldn't have seen, the people we wouldn't have met, the adventures we wouldn't have had, the expanded attitudes and horizons that we wouldn't have had the chance to understand, all over mainland Europe, would have costs us a fortune as humans, as people.

We've got about 15 GOOD summers left. I do not intend to waste them sitting in a tiny semi, whilst daytime TV dribbles down my front, on some small rule-ridden, expensive, small-thinking rainswept little island when there is the whole world to see before we shuffle off.