kijiji is a good start.
you need a helmet, riding boots, riding pants, and a crop( if your horse is slow ). you can find these things at the store Horsing Around.
as long as they are strong boots
There are several places that sell horse and rider gear. I use Dover Saddlery, since I am an English rider, but there are also other stores, like Horse and Rider. You can probably find a location near you on a store's website. Also, if you no what size you need, you can consider buying online.
shoes with a small heel riding boots or jodphur boots are best
longer riding boots are better in my opinion as they make riding more comfortable for both horse and rider. Your appearance also looks much better with longer boots.
Boots or sneakers.
I would reccomend Dover Saddlery
The tall riding boots of today are the ancestors of boots worn by 17th century British soldiers. On the battlefield these tall boots protected the lower legs and gave the soldiers better contact with the horse's side.
$40 to $400 in Australia
One can purchase men's riding boots from many different places online and offline. One can get them from Amazon, Ebay, and any other horse riding business.
A saddle, saddle pad/blanket, bridle with appropriate bit, stirrups, riding helmet, jeans or riding pants, chaps or half chaps if you do not use tall boots, riding boots.
If your horse is scraching it's back feet when riding you need to either get splint boots or bell boots. Look it Up...