Getting a bank account in Gran Canaria is a doddle if you have an NIE or residencia. Just pick a bank and give them your NIE number, passport and a proof of address (utility bill, rent contract). Then sign a lot of bits of paper and you have an account.
Buying a property in Gran Canaria costs about 10% of the price you pay once you factor in taxes and fees. Selling a property involves some costs but these only add up if you profit from the sale. The annual tax burden of owning a property in Gran Canaria is low.
Teaching English has always been one of the main ways foreign residents have lived and paid their way in Gran Canaria. While things are getting hard for unqualified teachers, there are always jobs around.