The unit you are looking for has a RRP of R6315. That being said you are looking for a second hand unit that will be cheaper, if you can find one.
I have 3 x Ai Hydra 26 HD units for sale, which in my opinion is a better unit. The RRP on these units are R8467. So kindly indicate if you would be interested as mine is a different unit and then we can start talking price.
PS On which tank are you looking to run the unit, what is the length of the tank?