I have an Abus D-lock with a plastic coated steel cable. I think it was around £50. It never really worked properly so I could frequently be seen standing at the side of a road in Bristol trying to get the key to engage with the lock. I still use it but it's intermittent at best.
My GF had bought a slightly smaller version of the same thing and it worked twice before she got stuck in Bristol and I had to ride down and spend about ten minutes trying to get the key to work. I even contemplated calling the non-emergency police line to explain that if they see someone hacking the lock off of her bike that the reason was that the lock had jammed. Definitely a situation you don't want to be in.
To be fair, Evans took the lock back immediately and replaced it with a Kryptonite Mini with a steel cable. So, not a good showing from Abus in our experience. I'd probably go for the Kryptonite one next myself.
The other lock I have, and love, is ironically an
Abus Frame Lock (also known as cafe locks) which I use if I literally nip in to a local shop. Quick and easy. No good for thieves with vans but there is no way you can ride the bike away. You'd have to carry it so it wouldn't take long for you to find them
Easy to fit and cheap. Just make sure you have the correct holes to accommodate it.