Sure I can but I didn't think it was necessary. I used to hand-write my notes, filling a £10 moleskine journal every month or so. Supernotes saves me £4 per month and I get the benefits of all of it's features.
You have no outgoings? Then sure, it's hard for me to suggest a comparison to you. I'm not sure it's up to me to suggest an analogy that works for every user on the internet however, pick something that you spend money on regularly.
It's £6 per month if you pay yearly. Also if you are a student you can get a 50% discount. Honestly it costs a negligible amount, that's less than a single day's worth of travel on the tube.