Low-cost (or no-cost?) CRM for a Veteran 501(c)19 org, 1,500 members and 5-10K leads probably

CRM for Veteran (VSO) 501(c)19 nonprofit with 1,500 members, 5,000+ leads
I'm looking for a solution to manage about 1,500 (1,012 active today, plus a few hundred inactive) members and at least 5,000 but hopefully more hot leads, that we'll be trying to convert to become members.
One big thing I anticipate is that we'd want to add new contact lists all the time, but to merge them with existing members or leads to prevent dups. Meaning, it's very likely that I'd get a list somehow, but it's not going to be a clean list … I'd expect a lot of duplicates with existing members and leads in the system. I don't want to lose the existing information, but I do want to add and keep any new contact information added (fresh phone numbers, emails, addresses)
I want to use the CRM in several ways:
Phone banking, to have volunteers use the CRM to check in on people and just to make sure they are doing well and are reachable. That's a key need!
Mass email by group. Main groups would be paid members, delinquent dues members, and non-members.
SMS/text messaging.
There's more of course but those are the big things. Budget is low, and if I can pull off a proof of concept using free tools that's ideal.