I waited til I felt more comfortable with Betta care before I expanded to the more expensive tail types. But now I have a veil tail, a crown tail and a new half moon.
Rusty was from Petsmart the other 2 were at Petco. If you feel fairly sure of your ability to take the best possible care of your betta I see no reason why you couldn't move on to a delta, crown, half moon or king betta. Those are what my Petco carry anyway.
As far as cleaning the tank... I live in an apartment and have full access to my stove but I just use the hot shower to clean the tank. It wouldn't take much vinegar maybe you can find someone who has some if you don't have access to the store. Bleach is something I bet someone has but you have to really really rinse that then let it sit in the sun for a couple days before you can even consider putting a fish in there. With the vinegar it's not that difficult (not that letting it sit by the window in the sun for a couple days is difficult but it's not as safe as fast). Good luck either way and I hope you will find a new one soon.