Elise shop ones are a pretty good alternative, I've just fitted those and with the right tool it took 20 minutes both sides. I couldn't however find the inner anywhere but luckily mine were easy to clean up before fitting. I've bought and fitted S2 also in the past and I'm fairly sure from memory they are even easier to fit but look more complex to manufacture. For a start they include both sides and a fixing to the rear. My man-math world say there is a saving but I'm not sure it's worth while, more a pocket money venture. That said I'm fairly sure they've increased possibly doubled in price since I bought them, I don't think I paid that much. Looking at the design I should imagine there is CAD work, tooling and jigs involved as well as prototyping, materials and man hours all of which have increased in price over the recent years, VAT too. Personally I couldn't be doing with the organising, selling and the sending side unless I did this sort of thing for a living. I am however interested to know whats involved in getting something like this to market.
Edit: Probably should have found the 2012 invoice first £76.90 for both S2 waist seals inc 20% VAT. Still that was 6 six years ago and you'd need to start from scratch I would have thought. What's the plan Foxy?