there are newer and better systems on the market that you can buy for that price that you can transfer to another car at a later date that have proper updated maps... look around there are loads of them
but if you really want the oem one it'll set you back at least 300 pounds and that is with everything that it needs except for the needed cabling from the back to the front that you will have to order from the dealer. .. making it very costly in the end so looking to an aftermarket one second hand is your best bet the likes of clarion/pioneer/sony/kenwood all have proper systems that do everything the oem headunit does and more