Not a Cobra, but this is the trailer I bought for the project. Cost me only $2500 with several months rego, which I thought was pretty good - it's several years old, the paint is a little rough, there's some minor corrosion and the mags are pointless. Spent this morning pulling the hubs apart and re-greasing the bearings (they were a bit dry, but ok) and checked the drum brakes which were pretty good. The only thing it needs is a missing mag wheel nut replacing and a spare tyre.
I like it because it's cheap, very lightweight (my family car aint much of a pack mule) and it comes with a winch. The next cheapest trailers started at about $3800 with licencing fees and went up to about 7k to get one made localy here in Townsville. Should be able to sell it for a similar ammount to what I paid once I don't need it anymore.