I think if you're taking time off work to roll bait then you should factor in £ p/hr. If you're doing it in the spare time, it's clearly better than sitting watching the TV doing nothing productive. I think if you frame your life in terms of your time equalling your work pay then it's not cost effective. In fact, everything you do in your spare time besides more paid work isn't cost effective in that sense.
Personally, I would say to try it but not because you want to save money. Do it because you want to explore the bait making experience. Do it because it's unknown to you and it's unnerving. Do it because learning about bait construction may give you key information which will help with many other things in life. Do it because it adds a further sense of adventure to your fishing. Do it because you clearly are intrigued by it and you'll be able to definitively answer the question of "What if?". Surely that's more important than saving a few quid? I certainly think it is! Imagine the laughs you're going to have, the elation the first time your bait catches a fish, the misery that comes from failures, and the joy of learning. Marvellous!