If you mean a mailing list, you don't need to do a paid giveaway at all.
You need a lead magnet.
A lead magnet is something you give away for free to list subscribers that is of high quality and value.
For example, on my hiking newsletter with is nearly 3K subscribers, I give away a guide to 35 awesome hikes that are not as known as others in the area. That's very valuable to my local and visiting audience.
I make sure all my CTAs offer that lead magnet.
When I send it, I also note that as a subscriber they'll get even more of those hiking trails throughout the emails they get. That helps to mitigate the snatch and unsubscribe actions that many list builders see. You have to make sure you keep pushing value with your newsletters.
My lead magnet is a PDF file that I created.
Free and simple.
If you don't want to offer a lead magnet, then you need to create the best copy possible to convince someone to subscribe based on the value you provide in your mailing list.
A lead magnet will make it a lot easier, though!