You have a lot of long-finned fish in your tank so I would say definately no for a male betta. I don't know if females nip other fish like males do, but I wouldn't get a male nor female with all of those long-finned fish in your current tank.
You could just buy a 1 gallon bowl at walmart for like $6.00 or a Kritter Keeper at walmart for about $5.00 and keep a betta in there.