Like others have already pointed out, I'm also not sure if giveaways are the best option since it might not attract genuine interest, which I assume is what you

Like others have already pointed out, I'm also not sure if giveaways are the best option since it might not attract genuine interest, which I assume is what you're after. Even though you might have the most insightful newsletter, getting awareness about this with a target audience can be tough. I'm not sure what the subject on your wife's newsletter is but, if she's not already, she should be active in the community targeting this audience. E.g. if there are discussion forums regarding the newsletter's subject then your wife should participate as an insightful and active member of this community and be viewed as an authority on the subject. Then having a newsletter sign up link in your public profile of these communities might then help in getting genuine subscribers.