If you can wait long enough you can usually find something at least reasonable. However, my rule of thumb is if you know you are going to need it eventually, snag it now if the budget permits. It seems like frequently either 'my' items just don't come around when I am looking for them, or they just got sold 2 minutes before I signed on . Of course, if you are not absolutely sure you're going to stick with a 4 ft tank, I can understand the hesitancy.
Bill