While Samba will work its pretty big and slow.
It is designed to allow you to work between machines with different operating systems....PC & Amiga, etc.
If you have only Amigas then netfs or envoy are more useful but you're right that envoy is commercial. I'm not sure about netfs since I got mine on the disk with my X-Surf card.
You might try simply setting up an FTP server on both machines and accessing each machine with an FTP client.
This would let you setup login passowords to keep things
more secure.....Samba would expose your Amiga to PC hackers, I think, since it is used in the PC world.
Sincerely,
--Wil Haslup