Running a contest is powerful way to explode your email list especially if you promote it via Facebook ads.
Just a few months ago, while surfing the intrnet, I ran a contest, spent $100 on Facebook ads and attracted more than 1,000 subscribers in 14 days. I wrote a whole post to explain how I did it now
With just $40 you should be able to get much more susbcribers than that (don’t spend all your cash on Facebook ads of course ;) ).