What about buying a piece of channel iron that is the wheelbase of your motorcycle, welding some drings onto it so you can strap the bike to the channel, and then add some rubber wheels to the channel itself?
The process would be to ride onto the channel, strap the bike down, and then winch the assembly into the trailer. Once in the trailer, secure the channel to keep the channel from moving. When you arrive at your destination, unhook the channel from the trailer, winch it back out, and then unhook the motorcycle from the channel. This will let you always load on flat ground, allow you to winch in and winch out, and will be as simple as slowly riding onto the channel on level ground.
I imagine a piece of channel is $20-$30, 4 tires from HD are probably $15, and a little bit of time to make an easy loader.
