Good on ya for having a go. It is a great sport and I'm sure you'll enjoy it. As I pointed out I'm not being negative, I'm just worried about the safety issue. I'm sure if you look around you'll be able to find someone to help you out with making a basic cage cheap. You may even find someone in this group that has a second hand cage for sale.....try it!
Don't get put off by getting lost in your first rally. It can be a little confusing but if the event is any good the organisers should give you plenty of time for the touring stages. Use it to make doubly sure of every instruction rather than panicking and rushing down the wrong road.
Good luck.