Suicide Squad. Perfectly encapsulating the spirit of the character, Robbie became an immediate fan-favorite and one of the most valuable assets WB had at their disposal. It's for that reason the studio explored a number of Harley-centric projects to develop, with Birds of Prey ultimately winning out.
The film hits theaters next year and Justice League fiasco notwithstanding). Obviously, there's hope Birds of Prey will be able to keep the hot streak going, and it sounds like it won't have to break any box office records to do so.
In a profile on Robbie, the film would have a smaller budget than other DC offerings.
The long-established general rule of thumb is that a film needs to earn twice its production budget at the worldwide box office in order to make back its money. If Birds of Prey really did cost $75 million, then its break even point is a measly $150 million, which seems like a figure it would be able to top in a single weekend. Harley Quinn was featured prominently in Suicide Squad's marketing campaign, and Sonic the Hedgehog.
In the last handful of years, 20th Century Fox proved that a studio doesn't need to spend $200 million in order to make a high-quality superhero movie (see: star Mary Elizabeth Winstead calling it "genuinely funny and weird" and something that could have come out of the 1990s. Since there isn't a fortune or the future of an entire shared universe riding on Birds of Prey, director Cathy Yan and company were able to play around more, hopefully making it a unique entry in the genre.
Source: Vogue