Yes Rufus is fine.
Linux is a free OS - you don't pay for it. Mint is available from their website:
Download - Linux Mint
Download the ISO, load it into Rufus, and you can boot off of it into a Live Environment. However anything you do will not
persist once rebooted (because it's running from RAM). So if you want to save any documents, pics, etc. while using the Live USB, you'll need to either save it onto the Surface Pro's storage (which is available to be saved to) or create a persistent Live USB (there's guides online on how to do this).