I don't have dental insurance either, but try not to let the cost of teeth cleaning keep me from going every 6 months. If I wait any longer than that, the plaque on my bottom teeth really starts to bother me.
What I do to try and save money is not have the x-rays taken as often. These can cost more than the cost of the teeth cleaning.
There is nothing better than how clean my teeth feel after getting them professionally cleaned and polished. Even though I brush more than once a day and try to floss several times a week, they never feel as good as they do after a trip to the dentist.