For myself, I only ever need a single roll of membrane, so that's £40, I already have the adhesive as I'll be using the same stuff to fix the tiles, no need for any of the band, simply cut a 200mm strip off the main sheet for internal corners. Domestic showers really only need 1m of tanking, especially over baths and in particular no more is needed unless using mosaic tiles. The OP didn't mention the polyester tape, that's £15 a roll, 2 required.
So to summarise, the OP could have popped a cherry on top of his eloquent reply, it's still not convnced me.
Remember, I have a choice as to what system I use, WP1 is gathering dust all round the country in shops, in fact, Topps stopped pushing it over 2 years ago, I needed to use some on a curved floor to wall joint in a wet room, two of my suppliers had WP1 in stock but it was out of date.
just read this one..
$40 bucks for a single roll mate..you need to find an other suppler there..your getting robbed...