I think you may have a hard job if you are looking at selling as a job lot, as most koi ponders would already have a filtration set up and koi, so they may only be interested in certain fish.

Then you may have someone intersted in the filtration but not the fish , but you will not be able to sell that until all the fish are sold.

As to koi prices it is not easy to tell without a good pic of the fish

The filtration I would say could go for around £200 to £250 possibly more.

Are there any koi clubs in your area that you could contact ? if not then possibly advertise them on a Koi forum . We have a for sale area in my forum, but it would help to have a rough location of where you are , eg county.

As to the cloudy water , do you happen to have any test kits to test the water with , there are a number of reasons for cloudy water high amonia /nitrite being two of them.