I bought A Halfords Advanced one two years ago for about £250-£300, very good and going strong. Folds up small enough to go in the boot whilst you are riding for the day, and doesn't take up too much room in the garage. Vertical dividers prevent bikes rubbing except some bikes that don't "tesselate" well - I just use some pipe lagging for protection there. Also you can tilt the whole thing backwards with 4 bikes on it to get access to the boot. Setting up and fitting to the car took me a pestering-child-free hour or so initially but thereafter it takes only 5-10minutes to get four bikes loaded up each time. Quick releases from the towbar in seconds.
Link here, come down in price to a penny under £200 at the minute
Halfords Advance Four bike carrier