Hi Duncan. As others have mentioned a 8" dob is probably your best bet. If you want new Bintel have the solid tube " BT202" for $600 or the Skywatcher collapsible 8" for $650 (which has a bonus eyepiece set thrown in at the moment). Both have all you need to get started and are reasonable quality. These are great value. A 8" can keep you happy for years.
Cheers Richard