Huge - not that huge. Pricey - yes.
Pentax: Diameter X length: 73 x 76 mm Filter size: 62mm Weight: 405 g Price: (B&H) $496
Fujifilm: Diameter X length: 76 x 98 mm Filter size: 67mm Weight: 490 g Price: (B&H) $899
Interestingly,
Fujifilm claim to have have solved the 'huffing and puffing' problem others have noticed with the Pentax 18-135 when mounted on a WR body:
"In order to improve the feel when adjusting zoom, a ventilator is placed in the interior of the bottom of the lens barrel. The structure effectively prevents dust particles and moisture from getting into the lens to allow for smooth operation."
I don't know how that feature matches up with the lens being WR though.