I made my own jumps. I believe a pair of plain standards cost less then $20. I made mine 4' - I don't usually jump bigger than 3'9" and then could use 8' lumber with no waste (and fit in the back of the truck neatly). Boxes and fill I made out of scraps from other projects but wouldn't have been much. Poles were the biggest expense and the hardest to find - round is not common at the lumber yard. I used bracing poles for fencing from the farm supply, not symetrical but cheap. Paint all came from the mistint bin at the hardware store. Don't forget to cut handles into the boxes. Paint your boxes a different pattern on each side so you get twice the jump so to speak. Use screws not nails so that you can replace parts when broken. Garage sales can be a great source of flowers, flowers leas from parties look great wrapped around standards to up the flower content.
I do know of one girl who built herself some schooling jumps and enjoyed it so much she turned it into a part time business and paid her way through university with it. have fun