I keep both bettas (though I only have one right now) and tarantulas, and my house is full of kritter keepers of various sizes that I use for both species.
Kritter keepers are great for transporting. I stay with my boyfriend on weekends and it's about half an hour by car each way. I use the keepers to move both my fish and my 4 t's (separately!). Another option for transportation is either deli cups or small plastic containers - melt a few holes in the lid with a hot nail for air and you're good to go.
Re filtration, with kritter keepers you need a high enough temp (78-80). I use 10w submersible heaters in my 1-3 gal keepers when room temp isn't enough. I've never had problems with melting plastic so far.
If you want to cut down on the water changes you can get 2-5 gal acrylic aquarium kits including power filters. I have a 2-gal (marina explorer) that was originally on my desk at the office. I've run it for years. It has a "bio-wheel" filter which has never made a sound. Doesn't have a light, though, and no place to put one. I'd recommend another model because of this.
In a 2-gal I change the water 50 - 75% twice a week. I'd suggest that even with this filtered setup you get a testing kit for ammonia (if not a master kit). It's a good way to establish the best water change schedule to minimize stress on your fish. IMO a master kit will pay for itself in fish which would have been lost to toxins built up in the water.