What happens if you exceed MailerLite's free subscriber limit?

Will MailerLite kick me off if I exceed their free subscriber limit? My subscribers just jumped from ~100 to ~450 from a giveaway I did, and while I don’t get very many organic subscribers (it’s mostly been people I’ve met in person) and so I’m not expecting to get over 500 without noticing/anticipating that… what happens if I do? And once I’m over 500, is MailerLite the most cost-effective option, or is there a better choice?