Geeze, for $400 I'll build you one. Or I can just give you some links and you can do it yourself.
First, do some reading.
http://ronreil.abana.org/design1.shtml
http://www.arscives.com/bladesign/forge.tutorial.htm
http://www.backyardmetalcasting.com/
Or you can buy you some real fancy ones:
http://www.hybridburners.com/new-ordering.html
If you have any problems locating supplies or have questions about the actual construction, chime in and ask.