Targeting a large radius and excluding a smaller radius
Does anyone know how to target one large radius (i.e. 100 miles) and exclude a smaller radius (i.e. 50 miles)? I ask because I'm working on advertising for a week long event in San Diego that attracts people worldwide. However, the farther you get from San Diego, the less likely people are going to come because of the expense. So, I'd like to put less money into those farther away.
Ergo, if I spend $2 on average (they're on Google Grants) for people within 50 miles of San Diego, I'd like to spend $1.50 on those within 150 miles but not those within 50 miles. Or am I just overthinking this?