Age has a bearing on this. One of the few advantages of growing old is that you can spend as much as you like on punting, because whatever you may have in the bank, it's unlikely you'll need it for anything else. Most of it will either go to the kids - who'll only waste it - or, more likely, in care home fees at £1,000 or more a week.
So you can either save that £150 to pay for another day in a care home - where you'll be ga-ga anyway - or spend it now on an hour with a succulent, young Brazilian hottie. Which makes it no decision at all, really.
When you've run out of money to pay the care home, the state has to pay; so in a sense, it's the
state who'll be paying for your Copacabana cutie, which will make her taste all the sweeter.