had my landlord replace water pump in three year old apartment plumber told us that pump itself cost 900euro, so it sounds like a reasonable quote to me although i expect that a lot depends on make of pump, size of apartment and other factors
You could look at power showers. They look like an ordinary electric shower, but instead of heating the water they take water from the hot tank and there is a pump inside the unit that boosts the water flow rate. They can be got for less than half the price you've been quoted, but wouldn't (I imagine) be quite as powerful.