Looking for New CRM Software to use but on a budget – Independent Book Publishing

Like a lot of others here, I was wondering what the best CRM would be for my small business? I was recently hired by a very small independent book publisher (literally just my boss and I in his basement) and we have been using hubspot's most basic plan but we're looking to potentially switch CRM programs we use. I am very new to all of this and I am the one in charge of marketing so I am still getting used to this role and my boss is incredibly technologically impaired so I could use advice.

I was wondering if anyone knew off the top of their head which CRM software offers the best plan for a small budget. I maxed that out in a week. Are we just SOL and going to have to pay a crazy amount no matter what?

Our main objective is building client lists and sending marketing information/ads but with our current subscription we have a very small limit of emails we're able to send monthly, which I maxed out within a week and half. However we do not have a large budget to spend on upgrading our plan significantly. I am looking at ConstantContact or MailChimp currently, and I'm leaning toward CC. For additional context – we currently have around 16,500 contacts (and growing) in total and we should be sending a couple thousand emails per week and our current plan maxes out around 3,000/month.