This can be one of the least expensive forms of offline advertising, especially if you are placing your flyer in a shop window somewhere.
With flyers or leaflets it would be down to you to place them yourself or to pay someone to place them for you. The only other cost involved is the printing of the flyer or leaflet.
I am sure you have come across leaflets left on your car windscreen in the past. There is no reason why you cannot do exactly the same at the local store or mall car parks.
Everyone out there is a potential customer to you. When you are placing flyers you have the best possible opportunity of picking up casual shoppers who don't use the internet a lot.
When you don't know a persons likes and dislikes you need to get the word out to as many people as possible.