Imagine an episode of The Antiques Roadshow where the objects are all gifts from your old partners and a price is put on their sentimental value. What might that faded T-shirt or once-loved mixtape be worth in cash terms?

In her performance The Ex-Boyfriend Yard Sale, currently at Camden People’s theatre in London, Haley McGee invites audiences to evaluate several presents from her exes. A coffeepot, a vintage typewriter, a guitar and a necklace are among the items displayed on plinths on the stage. When McGee reveals more intimate information about each relationship, we raise or lower our valuations accordingly. It all starts to feel like an alarmingly personal version of The Price Is Right.

The show, McGee says, was partly inspired by a £10,000 Visa bill she needed to clear after she moved to the UK from Canada. Looking around her home, she wondered what she could earn from selling off the old gifts and asked herself how much they meant to her and whether she could create a kind of algorithm to measure sentimental value.

Working with mathematician Melanie Phillips, who also makes interactive games, she established a dizzyingly complex formula that is outlined in the show. Part of the formula, the “relationship index”, measures her time with each ex on a scale of one to 10, including “how hard they made you laugh, the ratio of fun-to-misery and how good the sex was”. There was one caveat: the number seven was not allowed because it was deemed a non-committal, “copout” number, she says, quoting the self-help author Tim Ferriss.

The audience’s perception of how much each item is worth is affected by other details that McGee shares such as how long the relationship lasted, who broke up with who, and how long it took her to get over it. When she reads from her teenage diary, it makes us re-evaluate an object in a new light.

Along the way McGee asks a host of intriguing questions about emotions and economics. Why should tradition dictate that an engagement ring cost three months’ salary? At one point she uses a sticker gun to put a price on her face and sits on a plinth herself. She later wraps herself up as a precious object in a scene involving several metres of bubblewrap, some elaborate choreography and a Tom Waits song.

When making the show, McGee got in touch with each of the exes. “I was mostly very moved by how open and generous they were,” she recalls. “I hadn’t really talked to some of them for a long time … A lot of them thought it was a cool idea and were supportive of it. One or two were less impressed and thought it was silly or self-indulgent.”

In the show, we hear snippets of her interviews with past boyfriends and, gradually, some of the objects are anthropomorphised. The coffeepot’s lid becomes a mouth and we start to attribute certain characteristics to each boyfriend based on the look and feel of the objects. The identity of each ex is protected and they are referred to by the name of the item. It’s a way of “being a little bit cheeky and reducing them to an object”, she explains. “I tried to have pseudonyms for them but then some of my exes chose their pseudonyms. Typewriter wanted to call himself Perry and Bicycle wanted to call himself Gary.” A couple of her old boyfriends donated to McGee’s crowdfunding campaign but none of them have watched the show yet. Bizarrely, one of her exes’ other exes has already been to see it.

McGee describes herself as a “third-generation yard-show aficionado” and says her mother, a molecular biologist, “forced me to take maths until I was 18 because she thought it was very important”. But she says she doesn’t have an intuitive feel for numbers. “I’m a pretty emotional person, so using logic for the first time to look at feelings of worthlessness was really compelling.” The show charts how love and money intersect on various scales. In one episode, a grumble about splitting a bill for brunch seems to become a barometer for a failing relationship. McGee says that, in an earlier draft, she was also interested in “the way that money can be used as a weapon at the end of a relationship”, such as in a divorce.

A previous incarnation of the show, staged in a space at Euston Station, which is near Camden People’s theatre, was an installation that McGee imagined as an “art gallery, auction house and yard sale smashed into each other”. Visitors listened to interviews with her exes and answered questions about their own relationships. As part of the project she crowdsourced a list of songs that people listened to on repeat after a break-up. The playlist – available online – is 472 songs long and growing.

The Ex-Boyfriend Yard Sale reveals McGee to be a funny and assured performer and it’s easy to imagine her hosting a popular television version of the show. She has several ideas on how to develop that; meanwhile, her stage version includes a salient figure about art and economics. In one of her many calculations scrawled on the wall of the theatre she reveals that the show designed to clear a £10,000 debt has so far made a loss of £7,627.

• The Ex-Boyfriend Yard Sale is at Camden People’s theatre, London, until 8 December.