Thats almost impossible to say....
Too many factors are involved...if your talking new then think small...100 gallon or less. possibly a 120 or 125 on sale...
Locally you can pick up a 100 gallon tank...stand...glass tops and lights for $189.00 plus tax.
Used? I've seen 240 gallon tanks...(tank only no accessories) go for that but it's hit and miss. I just missed a FREE 125 gallon tank...stand, canope, lights, gravel and wet/dry by an hour or so from some people moving to the midwest. You just never know...