I have been able to get the steel for 250$. I figure I work in a scene shop and will practice welding. Or for the cost of beer get a helper. Time excluded, this seem much cheeper than the 750$ I would have spent on a new trailer. The estimated weight is 450#.
I'm still going for 5X10 raised above a lower deck for added storage.
Now I need to learn all I can about axles and weight distibution.