Need multiple opt-in forms for different email lists on a single site

Hi Guys! I’m hoping you may be able to provide the best solution for my needs.

I currently have 2 opt-in forms, each utilizing different lists within MailChimp. The MailChimp for WP plugin only allows me to create one form for a single list. I also need to create a pop-up form to send users to a separate list, and there’s potential to need to create additional MailChimp lists to coincide with additional opt-in forms.

In your experience, what would be the best plugin for me to use to achieve my desired results? Being able to create multiple places for sign ups and sending users to different lists is important for my clients business needs. Ideally, I would like to use a free plugin or low-cost, as this is a workaround to save money for a new business vs. using ConvertKit, until my client can justify spending more on professional services.

I appreciate the feedback!