I have a Python. Mine was $65.00 CAN. It's very easy to use, one end goes in the tank the other end gets attached to a faucet spigot. It has a mechanism in it that when you turn on the tap, it creates an automatic suction and will start removing water from your tank. If you leave the water on, the suction is more powerful but I just turn it off and let the water flow out naturally,( I hate wasting water). You can use the gravel vac on it or just use it to remove water. When you want to fill the tank back up, all you do is add de-chlor to the tank first then adjust the nozzle so that it makes the tap water go into your tank. (I always fiddle with the water so I make sure it's the right temp first).I have a 140g so I can't imagine using anything else! It's very easy to use and a major time saver, plus no having to get tank water in your mouth!
I'm sure there are other vacs like the Python so maybe someone can chime in with that.
Good luck