I was planning on buying acrylic, but if I find a used glass aquarium for a good deal how would I ever move it?
You can move either by yourself easily using a contractors appliance dolly with cam-strap. The whole tank weight will be on the glass tank's short and back long panel supported by the steel frame and cam-strap of the dolly balanced on the wheels making the weight easy to move, pickup and lay down. Under no circumstances use people to move a huge glass tank, one trip and everyone will lose balance and drop-crack the tank. I picked up a used contractors dolly on CL for $5 normally $200 for the model I have. You can even rent them with motorized climbing wheels for stairs if the item is in excess of 800 lbs. But I thing a 300 glass weighs no more the 400 pounds empty and more likely 300 pounds if not a tall tank but long and short. If you mean full of water you'll need add another zero to the weight use a crane.