Express Post does qualify for seller protection, it's only the pre-paid 500gm and 3kg satchels that don't. All other express services give you documentation that meets PayPal's requirements for selller protection. 

A <500gm parcel costs the same as a 500gm regular satchel, so while I don't offer express as standard, I use my own packaging (costing around 40c), then pay for express at the counter to get the lodgement form filled out and stamped. 

C&S will hopefully be adding the promised express service soon, then I (and perhaps many other sellers) will be including as an option on all my listings.