I say go for it! Rescuing bettas is one of the most rewarding things I have ever done, because you know you are making a difference in their lives. I don't get my fish for free (I'm worried they'll refuse to let me have the fish at all, plus I'm super shy) but I'm working on getting the courage to ask. If you do decide to rescue, you'll be glad you did. :)
Kindness and respect should be shown to all animals, no matter if they are furry, scaly, big, or small. Be a hero to the animals and GO VEGAN!