Xbox 360 slim 4 gb upgrade options

What's the cheapest way to get more storage officially? (It's not for me)

Thanks

Depends how much storage you want. If you just need a little bit, the easiest was is just to stick a USB flash drive in the front. Think anything up to 16GB will work. If you need more than that then a replacement hard drive is in order. You don't specifically need to buy the slim model hard drives, if you go for the old one just take the outer case off, the hard drive is the same inside. CEX sell them starting from £10.