I don't think you will find a cheaper alternative, the dealers have it well stitched up on anything to do with auto security.

You might see key blanks on ebay but they don't guarantee that all the key functions will work when they're cut, it might even be that they will only work the actual physical mechanical part of the lock, so you still need to access the security data from the factory data via the dealer for the car to accept it as a valid key, and they won't do that for just a couple of quid and a smile.

My VW replacement last year cost just under £200, if I'd faffed around with an ebay key I'd only have saved about £30.

Don't even think about cutting corners here.

Your car key doesn't just unlock the doors & start the engine these days, they control the rolling codes for the alarm, and hold data for use during servicing, such as fluid levels & odometer readings etc

Get a fresh key from the dealer or authorised key cutter

£270 is still cheaper than a new car, and only having one key is a great inconvenience and can cost a lot more if you find yourself with no key at all.

Remember the days when you just jotted down the number around the ignition barrel in the dash and got a ready cut key off a big keyboard at the dealers?

It was so much less bother for car thieves then:)