Think perspex would be the better and cheaper option. Very quickly fabricated, better finish than 3d printed and can be remachined if the dimensions needed to be changed. Also probably ~$30 in cost too and ten minutes work.@LukehGee - I'm not set on any specific material so 3D would certainly be an option, and Id be more than happy to accept your offer of modelling it up, that would be brilliant - thanks!
Great idea about adding or replacing the shelf in a cupboard with a perspex one. So wish I had shelves or cupboards above my bathroom sink to do this.