There are worse ways of filling the weekend viewing schedules than a charity event like last Saturday's Sport Relief "Go the extra Mile" fundraiser. And there are worse ways of massaging celebrity egos than by allowing them to parade their social consciences on the little screen on behalf of people less publicity-hungry than themselves.

I just wish we'd charge them a proper rate for our services.

Across the UK, according to the BBC, some 81,000 of us took part in 144 official races in the "biggest mile event in history". Ten thousand of us, including Prince William (who failed to break the six-minute barrier despite all his advantages of birth, breeding and starting at the front), did the run on London's Embankment. We raised what the organisers describe as "a record £11,078,359" on the day. And the BBC transmitted five hours of programmes for the event.

These included an interview with England's penalty-misser-in-chief, David Beckham, by the Fast Show's Ron Manager, aka comedian Paul Whitehouse. Beckham, it was generally agreed, had been an all-round "good sport" by submitting himself to jokes about those penalty misses, his high-pitched voice, his love of "bling", text-sex messages - and "holding his own" in the dressing room. The one question that was presumably off-limits, as it always seems to be on these occasions, was how much of his own money he'd put into the Sport Relief appeal.

The same was true of the trip to Peru on behalf of Sport Relief by Beckham's wife, Victoria, which featured in the BBC's documentary A Mile in Their Shoes. "I feel so sad and helpless, yet I really want to help," said Victoria, after spending time with 11-year-old Dinah, whose mum died three years ago and who lives and works with her dad on a rubbish tip - or at least did until the Sport Relief-supported charity ChildHope came up with the cash to enable her to go to school.

"People shouldn't have to live like this," Victorian commented. "I'm finding that everything I've seen and experienced is taking its toll on me - as it would any mum."

Now I'm not going to join the "former Spice Girl seeks to revive flagging image with public sympathy from charity work" knocking crew. Better a picture opportunity of Posh Spice bringing public attention to bear on the plight of Lima's quarter of a million working children under the age of 12 than yet another shallow photo shoot publicising some unnecessary product or other in the Beckhams' extravagant consumerist lifestyle.

But why don't we charge our celebrities to take part in these sorts of things, rather than, as is so often the case, allow them at a minimum to milk us for every penny of expenses they can possibly claim - or at a maximum to impose "appearance fees" that are usually more than most beneficiaries of the particular charity appeal in question earn in a year?

The rich and celebrity-famous owe us at least this much. Their wealth and fame, after all, comes from us. They clearly feel some guilt at not having earned it. (What else, other than guilt about unmerited riches, makes questioning someone about their money the last taboo in celebrity interviewing?) And they clearly feel some need to absolve themselves through good deeds.

So why not put a price on their absolution, as the church used to in medieval times with its sale of indulgences for the forgiveness of sins? David Beckham wants to turn his cheating on his wife with his former PA, Rebecca Loos, into a joke about "textual intercourse"? Fine. How much is that Vodafone sponsorship worth again, David?

Victoria really really wants to help Peru's poor children and not feel so "sad and helpless" about their situation? No problem. How about (as a down payment, of course - we'll talk final terms later) something like the £100,000 you laid out for that statue of baby Brooklyn posing with you and his dad?

We should be careful, though, lest the sale of celebrity indulgences is done too cheaply. This year's Sport Relief event sold its principal sponsorship slot to a chain of gyms for about what the Beckhams earn in a week. For around £250,000, the company got its name listed even ahead of Sport Relief itself in the 144 official Fitness First Sport Relief Miles held around the country. With five hours of prime-time television to accompany the races, you can't help but feel that the Fitness First folk bought themselves a bloody good deal.

The truth is that celebrity and corporate support for charity is built upon a con-trick. We, the charity-supporting public (whose generosity declines in direct proportion to the size of our income), are being taken for a ride by people who want wealth with a clear conscience - but are not prepared to pay for it.

The money raised by events such as Sport Relief makes a big difference to people's lives - and not only those of Peruvian children lucky enough to have their photos taken with a British pop star. But it's a mere fraction of what the celebrities alone could contribute if they wished.

I wonder, did anyone from Sport Relief make the obvious point to Victoria Beckham that the poor are poor because the rich are rich? And nowhere more so than in Latin America, where a recent report by Merrill Lynch and CapGemini revealed that the very rich have a higher average wealth than any other major region in the world.