The cost to try it is time. Take a laptop you can afford to wipe, install Linux Mint Cinnamon, and just see how you like it.
But in your specific use-case, I do not expect this is a good idea. You are not going to save money on any scale that matters to a law firm. You can run LibreOffice on Windows just fine, and if it doesn’t work out, you can rent Office 365 (Dollars A Year). You’re not in a profession where FOSS tools like Blender and GIMP might displace obscenely-expensive industry standards.
What free-as-in-speech software might mean to you is control. Windows 10 does some dumb shit. Windows 11 is even worse and getting worse… er. Even more worse? Even dumber. Linux distros and open-source programs are made by the kind of ultranerds who said “absolutely not” and are limited to problems entirely of our own creation.