From my experience the GSO 2" Quartz SCT diagonal is probably the best value in quality diagonals without going for Big name brands like Televue.
Andrews list this at AUD119.
To use this diagonal for a refractor you need a spare standard GSO 2" EP nosepiece. Just unscrew the SCT adaptor and screw in the nosepiece when you want to use it for a refractor.
However if you want dedicated 2" diagonals for each scope buy the GSO SCT version and the Williams Optics 2" Durabright Diagonal (fits 2" nosepiece only) has the best close tolerance fit eyepieces and camera adaptors. USD149
http://www.williamoptics.com/wo_shop...roducts_id=545
David