I would recommend a new case if youre 100% set on watercooling, seeing as the manufacturer says yours is not capable - I would have thought it meant any water cooling, due to the fact is lacks adequate space for a radiator or tube holes.
Again though, in order to suggest a good case theres a couple of things that we'll need to know:
1) What are your chosen upgrades? (what Graphics card are you getting, psu etc)
2) What is your budget for a case?
If your case does have the rubber flapped holes in the back, it usually indicates that its compatible with water cooling.. even though the website denies it, it might be worth heading over to their forums and seeing if anyone has your case an knows for certain.
Unfortunately I know of none within that price range - Cases that support Water cooling tend to be more high end and therefore more expensive, usually around the $100+ mark.
To be honest, with your current system there really is no need for Water cooling, seeing as Air cooler will be more than capable of handling an overclocked 2500k - providing you don't live the Bahamas.