Eye Watering

I've been using Optrex Eye Drops for years now.  I find them quite refreshing in a morning, and soothing at night - but - the prices are rising.
Boots now charge £5.00 for 10 cl - this equates to an eye watering £500 per litre.  Sainsbury's are £4.70 (£470 per litre).
Checking the ingredients I find that Purified Water is by far the biggest content followed by Witch Hazel (13%) and then 4 other minor ingredients.
Not bad - selling water at almost £500 a litre. 
(My 'research' revealed Amazon have the same for £3.67 (£367 per litre) - cheaper, but still a rip-off).