@DavBot good thinking. I always advise that a bike lock should cost about 15-20% of the cost of the bike. Also, make sure when you lock it up that you lock the wheels to the frame. I used to use two locks. One to lock it to whatever I was locking it to, and another to lock the wheels to the frame.
And trust me, it paid off. There were a few times where I could tell someone with a bolt cutter failed to get my bike. You don't question the cost of the lock after that.