Well, quite a lot, actually. Log on to www.supperwiththestars.co.uk and, for as little as £300, After They Were Famous types such as Linda Lusardi, Tony Hadley and Limahl will be happy to pop over and make small talk with your dinner-party guests. Want an autograph? No problem. Head to Autographica, “the world’s largest autograph show”, at Heathrow this autumn and you’ll find the likes of Val Kilmer and, er, Patrick Moore doing the honours from £5 a pop.

And there’s worse. Next month, Celebrity Messages launches its portfolio of “artists”, including Vinnie Jones, Tara P-T and Caprice. Just £3.50 gets you a recorded birthday greeting or wake-up call from your favourite celeb. Caprice was so taken with the idea of “reaching out to her fans” that she recorded 300 individual messages to cover all eventualities: “Hi Barry, this is Caprice”, “Hi Darren”, and so on.

Stars who turn down extracurricular work are a dying breed. Most will eventually sell out, even if they don’t need the money. Take David Beckham, the king of celebrity branding, who has pocketed an estimated £30m for fronting Gillette’s ad campaign. Or Enrique Iglesias, who is rumoured to have accepted more than £100,000 (plus expenses) last summer, just to sing a ditty or two at a party in Marrakesh. As for Jordan, well, she could afford to buy new boobs every day for the rest of her life with the £1.75m she is set to pocket from OK! for the rights to her wedding pictures.

“All celebrities are prostitutes to a large extent,” says Richard Brecker, of the celebrity brokers Upfront. “They all have a price — they’re all shrewd business people. Their fame is not going to last for ever. It’s smart to cash in while they can.”

You’d think the moonlighting celebs would be laughing all the way to the bank — but quite who has the last laugh is open to debate. Who hasn’t chuckled at the sight of Mel Sykes conquering her dandruff by endorsing Head & Shoulders, and Stirling Moss going soft on us as a front man for erectile dysfunction?

For pure A-list-standard satisfaction, however, take a look at www.japander.com, which exposes erstwhile heroes such as Natalie Portman, George Clooney and Harrison Ford making big bucks in Japan — by promoting products they would never touch at home. As the brand publicist Mark Borkowski says: “When celebrities get caught out, the world becomes a very small place.”

The sad truth is that the role models and icons of old have been replaced by $ellebrities, a term coined by the American advertising titan George Lois in 2003. “What are you doing?” he asked. “Why are you using celebrity in such a completely boring way?” It was a point made in the 1960s by the social historian Daniel Boorstin. He predicted “an age of contrivance dominated by counterfeit people celebrities. Celebrityhood no longer requires genius, heroism, lifelong achievement or unique talent. It can be made a commodity and sold at the checkout counter at grocery stores”. This, he argued, would spawn a culture in which little meant anything and little mattered.

Which is pretty much where we are now — and why every reality-show wannabe and dire has-been is milking their fame for all it is worth. “This is a good time to be a celebrity, from a commercial point of view,” says Brecker. “The rules have changed and the definition of celebrity has widened. Since Howard from the Halifax ad arrived, anyone can be famous. But it’s a sad time to be a celebrity in terms of magic. Nobody is special any more, because the idea of celebrity is devalued. Now, there are fewer genuine celebrities with real talent.”

All this means that, while there are ever-growing numbers of celebs trying to sell us a piece of themselves, we are becoming increasingly disinclined to buy. Add to that the low-ratings knockout of Celebrity Wrestling and widespread disdain for Celebrity Love Island, and saturation point is nigh. “The public is more switched on and less forgiving now,” says Borkowski. “They’re sick and tired of the here-today and gone-tomorrow celebrity culture. Celebrity worship is over.”

Ultimately, of course, cheap is a state of mind. It is what separates the true stars from the wannabes. We will still pay top dollar for what we can’t have, which is why the golden rule of fame is “keep yourself expensive”. That doesn’t just mean adding a few noughts to your price tag. It’s about saying yes to Chanel, but no, no, no to Pedigree Chum and Always pantyliners.

After all, you’d never get Nicole Kidman signing up to whisper “wakey-wakey” from your mobile, or Kate Moss trying to flog you haemorrhoid cream, would you? There are some things that money just can’t buy.

Times recommends

• Live chat: Thrifty ways to update your winter wardrobe
• Is anybody out there really listening?
• Nutrition Q&A: Will eating late make me fat?