This is common struggle I face with our growing email list at my current employer. I'll start by saying that email is still the best way to reach customers in my opinion.

I would first recommend that you segment your list in 3 areas.

1. Recent subscribers (within 60 days - does not matter yet if they've opened an email or not)
2. Engaged subscribers (on your list for more than 60 days and have opened/clicked on your campaigns)
3. Lapsing subscribers - On your list for more than 60 days without opening an email.

What this does is allow you to tailor your message depending on the list. In some cases you can even decide to send less to the Lapsing subscribers (for example) since they need more nurturing (a more aggressive subject line, more enticing offer).

Facebook is another way to get your message across. This was mentioned in another answer and it is 100% true. You can easily build an audience and use the same segments you created above to match your budgets to your segments. This way you spend smart.

Happy to hop on a call with you. I'm offering it for free as I am new on Clarity but have over 10 years experience in email marketing.
https://clarity.fm/morrisshipper/freebie

Thanks!
Morris