hi Topher
I would think that negotiating a lower price would be unlikely as I am not aware of anyone else managing to do this, despite significant delays, lack of facilities etc and I don't think they would like to set a precedent.
Chucking in your deposit and walking away may not be that simple, as Calidona have threatened to take those who don't complete to court, to get the outstanding sum.
There is the option of taking them to court for failure to fullfil their side of the contract , due to late delvery, unfair contract (no completion date in absolute terms), failure to provide facilities as promised etc
unfortunately no simple options
kev