Any chance you could run this through the ol' spreadsheet...
1. 2006 Mazda MX-5 2.0L Sport 6sp Manual, 57,000 miles, No aircon
2. UK Market (Dealer) value £7,500 - £8,500
3. Aus Market value (best guess on this because the exact model names differ somewhat) Private price $19,800 - $22,500
Cheers.