Congrats on the pass.
Genuine Nissan Boots are of considerably better quality than the aftermarket ones but I agree that the price isn't justified. On a £ per year value they're probably about right! Genuine boot will last >10yrs and cost big bucks eg the £100 you were quoted, aftermarket will be a few tens and last a few years and can be a poorer fit.
One brand to steer clear of is Firstline but fortunately I don't think they make CV Boots...yet.
The rubber compound is so poor that you can fit a drop link and the balljoint dust boot can perish and split within 2 months. That was 6 years ago and they still haven't changed the rubber compound as I still see it happening at work!