I bought a Bosch Aquatak from ebay about 5 years ago for £40, gets used a few times a month and hasn't failed me yet.
I'd avoid cheap Karchers if I were you. Get a Nilfisk instead. Karchers use plastic pumps in their cheap models and they are prone to failure. Nilfisk come with 3yr guarantees from
some places so good on that front - also have recently got one myself and am very impressed