Where can i find the cheapest 50+ gallon tanks. websites, stores, etc. (just the tank and lights or just tanks).

Ismael, you can try the classifieds in your local paper, Craigslist.com (then find your particular area), or even wanted notes in pet stores. I have seen tanks in second hand stores as well here, but that probably depends on your location.
Oh, and one more great source - Aquabid.com....