As a guide, just 1 year ago I bought 16 sheets of FI FI48 Rigid Glasswool Sheets 2400x1200x25mm for $300.
I'd bought 50mm over 10 years ago, and think the current pricing is 'relatively' cheaper.
I've also seen Knauf have similar spec SemiRigid sheets, but don't know all the relevant specs, so went for Fletcher as it is for all intents the same as the OC7xx .