I am a photographer and do many magazines which are NOT Vogue and sometimes very low budget magazines.
My experience is that when I travel somewhere, I usually call up the magazine before, they mention a stylist that they work with and I plan the concept with the stylist and whatever it is displayed in the magazine has more to do with the influence of the stylist, who is the model that is being used and who is photographing because a lot of the shops that let the stylists get the clothes (NEVER FOR PAY) weights how much exposition they will get from the shoot. Because in credits a lot of the times it will say: Such and such model is wearing dress by such and such designer at such and such shop.
But I also take shoots to do outside the area of the magazine, for example, I have taken Elle Bulgaria and done in Brazil. There we were shooting with Caroline Francischini and Laryssa Castro and we were pretty much free to choose the styling, but sometimes some of the magazines send me a list of brands that I have to stay within when working with a stylist that is of my choice and the magazine has never worked with.
In other words, could be that the magazines only use clothes of advertisers, but either way I have never heard of stylists paying to get clothes in editorials in magazines, for the opposite. Most of the times, the brands and the shops are just too happy to let them borrow so they can get the free advertising that will come with the exposition of their product in the editorial pages. And the not so famous designers are even more eager to let all publications use their clothes for the shoot.
If a small or big designer should ever ask me to pay for using their clothes in a shoot I will tell them that they are CRAZY and move on to other designers, because there will be plenty that understand the business and will never charge!