Step 1 - Get something over or in the hole, quickly. A sail, cushion, whatever- just slow the flow somehow. No pump that fits on board will cope with a major
hull breach!
Step 2 - Start getting the water out so you can reach and stem the leak.
A 10,000 GPH gas powered emergency pump can easily be found for $200 to $350 (CDN/USD). A failed 2" seacock, three feet down, won't keep up with this pump.
A 25,000 GPH model starts at about $500, and will clear the
bilge with a 3" through-hull broken off three to five feet down.
If you have hydraulics and trust your main
engine, similar flow rates can be obtained with an industrial/agricultural pump like a Pacer S-series coupled to a hydraulic
motor. Or if you want a fully independent
diesel pump, couple one of these to a $600 air-cooled 10 hp
diesel.
Any of these pumps have flow and pressure good enough for effective fire-fighting. They're also great for wash-down, special
events (welcoming foreign
boats, etc.), dealing with charterers who
anchor too close, etc.
Yes, you have to add suction and discharge lines to those costs. But it's still pretty
cheap compared to what some folks spend on
furling gear, nav
computers,
wind turbines and other useful cruising gear.
(Of course, it's best to keep the
hull intact, the seacocks working, and have watertight bulkheads in the high-risk areas- but the thread's about emergency pumping, i.e. what to do when all that prevention still isn't enough. The priority must be to find and fill the hole, by whatever means necessary- the pump's immediate purpose is to stop the
boat from sinking while you do that.)