If cost is your factor for deciding size, then would suggest keeping an eye out for used tank (fresh or salt) from someone leaving hobby. Craigslist, etc. This below link might help you find club local to you where perhaps they also have a sales forum but no shipping worries if local:
Looking for some locals to share frags and info with? This is the place! Find a local club that meets in your area! If you want to add your club just contact us.