By far the cheapest method would be to hire a van and transport the stuff yourself.
You will be limited to the size of van you can hire by your driving licence, and you will need to inform the hire company that you are traveling to Germany. You will almost certainly not get a one way hire, and so have to bring the van back. You will also need assistance to load/unload the van (but that’s what friends are for).
But since you will not be paying the wages of at least two people to pack/unpack and travel to and from Germany – you will save yourself a packet.