I have been passed the details of a manufacturer in Perth - John Papas Trailers.

Rough quotation for new Red Witch trailer, fully hot-dipped galvanised but not licensed for road is $2800. Plus you need to make your own carpeted boards for the hull to rest in.

Not sure what the delivery price to Victoria would be like or whether they would give the plans to someone more local for you.

I have a name of someone to speak to there. If that would be helpful, send me a PM.