You have a Mercury engined boat. Ideas...
Check Crowley Marine:
http://www.crowleymarine.com/powerheads/mercury_mariner/siz_cylinder.cfm
They are the most prominent Mercury rebuilder I know of. Sort of the SBT of bigger boat engines.
The earlier respondent was correct. A rebuilt powerhead for your engine will be in the range of $4000-6000. These engines are great but if you blow the block things get expensive fast. It may not be worth spending that much on a 10+ year old boat.
Idea: It's often cheaper to buy a replacement engine with a boat wrapped around it. I just watched a Challenger 2000 sell for $5700 on eBay and it was advertised as being in great shape. Lots of boats have significant hull damage after storms, so you might be able to pick up a cosmetically damaged boat for even less - indeed, less than the engine alone would cost!
That would give you an entire engine/jetdrive plus lots of spare parts. It also increases the likelihood that you'll find an engine, because you don't have to find an exact match - anything with your engine is fine. Several models of the Mercury SportJets have been installed in several models of Seadoos and Sugar Sands boats for many years, so there are a lot of them out there.
Finally, I agree with the idea of parting it out if you don't decide to fix it. I'd personally be interested in a few engine components, and possibly even components of the boat itself (I too have a C2K). You could even part out the stuff you don't need if you go the "buy a broken boat for its engine" route, thereby recovering some of the expense.
Report back on what you find and decide!