75 is prolly on the cheap end. Based on your dimensions its a 55g tank which go for anywhere from 150-200 .Sometimes you can find them cheaper but not always. Tank condition plays a lot in what a person wants to pay. I think your 3d background in that tank could up the price a bit. They are fairly cheap to do from scratch but its a decent amount of work that goes into one. That driftwood which was probably purchased was a good 20 bucks plus the cave and water bowls. That being said, if someone gave me a free 55g I'd put a critter or fish in it.