I've not been to Bratislava, so not looked up any agencies in the city, but the prices you quote are ludicrous for that part of the world. My suggestion is that you search for agencies based in Prague, who will be able to arrange a companion for you, as they have girls based in Slovakia. For a trip of 4-5 days, the cost will average out at more like €500 per 24 hours, and you'll have a tour guide to show you around.