Depends on the rules in your state.
In GA, when a person pays to win something, it is considered gambling. However, charities (such as most VA Bingo Lodges), schools, etc..., are required to register with the state before they can do such. You need to look into the rules of your state. Member only type lotteries fall into a catch 22 situation. Even though, the member is "NOT" required to purchase anything to win, the state may look at it differently, if "Non-members" are not allowed to win. For example, the contests that Pepsi & Coke (among a few to mention) will allow you to receive a playable game card for the chance to win via mail without you purchasing their product. Now, in GA, if you are required to purchase a product and/or be a member, it is usually considered illegal.
I would suggest you do some searches in your state's laws to make a determination to what the rules are. Most states are reasonably clear about the rules.
Good Luck
Sir Metro