Class one initial is quite expensive, but after that each section is valid for a different period of time, so each yearly renewal costs a slightly different amount.
Also, if you get a class one, and after a year you don't renew, you still have class 2 privilages for 5 years (as you would if you just get a class 2)
You don't want to do all your training, then find out you can't get a class 1 medical for whatever reason. It's worth getting it just for the peace of mind.