Take a look to see how I made it in action. I recommend you to ask for help (you need more hands)!
If you want to buy it cheap from china for 24$:
Step 1: How It's Done..
Cut the kapton tape so it fits the size.
Clean your bed well ( the aluminum one :P ).
Spray some water on the bed after you put something around it, so nothing gets wet.
With some help put the tape from the back of the bed and let someone hold the other side, then start using a card to take out the air and water bubbles.
Cut the edges. Dry everything very well!
And happy printing!