How do you buy a billboard?

There are two ways I can answer this, and I'll provide both answers. If by "buy a billboard" you mean you want to advertise on one, you've got to contract with at least two companies--an advertising agency to design the campaign, and a billboard company to display it. (You might also have to contract with a modeling agency, a photographer and a stylist, if there are going to be pictures of people on your billboard.) You will pay the advertising agency once. You will pay the modeling agency, photographer and stylist once. You will rent the billboard in 30-day increments, if it's a printed billboard. The new digital boards can probably be bought for just a few days--like if you already have a campaign running for a concert, and you want to use one of the few digital posters in town for the last couple of days before the event to really try to get people to come to the show. Billboard pricing is like any other real estate: location (city it's in), location (where in town it is--a billboard that 3000 people drive by a day sells for less than one on the Interstate where 10,000 people drive past it a day), location (a billboard near a school sells for less than one out on the interstate no matter how many people drive past it a day, because it's harder to sell it--there are many things, like beer, you can't put on a billboard next to a school). If you're trying to buy the physical billboard...don't. You can't own just one--an advertiser wants to buy multiple billboards, which someone who owns exactly one can't offer. A national advertiser will buy billboards all over the country. And there's a LOT of zoning and regulatory stuff involved.