I've done a fair amount of searching and can't find a straight answer anywhere.
The free tiers on most of what I've tried are basically useless. You get just enough to see that real people are there, then hit a wall the second you try to actually message anyone.
The account verification process tells you everything. Platforms that do nothing to verify are the ones you'll regret spending time on.
If you've got experience with any platforms or approaches that work, drop them below.