Hajimemashite, ryous-san! Yes, you can do short sentences akin to the ones you mentioned; like: "Buy two, get one for free!" "Get five for the price of three!" Or, for the real short version, just: "5 for the price of 2!" Especially in ads, I'd say using numbers like that is probably better, as the difference between the two is immediately apparent to the brain.

hi, when you run an advertisement, it's important the context of your campaign as this will play the role of telling to the customers what your company is offering. don't worry too much on your grammar. sometimes, a crazy advertisement draws a lot of customers than those of formal one. Mark Kramer & Jura's example are perfectly fine. you just need to higlight some words such as FREE, TAKE 1, 5, GET. this will definitely catch everyone's attention. you can also go with this advertisement: "GET 3 for $0.99" (assuming that the item will cost them $0.50 = 'Buy 2, Get 1 FREE'). notice also that instead of advertising the price at $1.00, I used $0.99 as this is more captivating (just like saying "GET 3 for LESS THAN a Dollar"). :)

Hi , adds for cosmetics and perfume often have these inducements as well. Example: Spend $70 on any Estee Lauder product and get this travel bag free or buy a Clarins moisturiser and get a free lipstick.