I made a makeshift cross country start box out of jump standards because my horse hates them. I don't know if this is a DIY :)
I would love to know how to build a makeshift dressage judges box out of stuff in the ring because my horse doesn't like those either...
I made a jump that looked like Nessy once. I went to the hardware store and bought drainage pipe for its neck, humps, and tail. I thought about going all out and buying dry ice for under the jump, but decided I'd want to live to see another day.
We are making saddle stands right now out of those wooden wire spools some companies give away. Just add boards under to keep from rolling and you can even add hooks on the round part to hang your bridle.
Also, I find a ton of stuff for my barn at the dollar store. I got those battery operated click on lights, white boards, and even clothes hooks to use as halter hooks.
Old boards are also awesome to paint stall signs on.
I made saddle racks, blanket bars and jump standards.
Saddle racks a simply a chunk of 4x4 about 2 feet long with a heavy duty "eye" screw in the end. On the wall, I mounted the "hook" portion so that I can hang the 4x4 perpendicular to the wall. The tension between the end of the 4x4 and the wall provides enough support for a saddle. They are also easy to take down when you don't need them.
I made blanket bars out of some 1.5" PVC pipe, some rope, a caribeaner and two "eye" screws. I cu the pipe to about a 3-3.5 foot length. Screw the two eyes into the wall about 3.5' apart and tie one end of the rope to one eye. Feed the rope through the pipe and tie the caribeaner or a clip on the end. You simply clip it to the second screw and voila, a blanket bar. These work great for saddle blankets, leg wraps and body blankets. I have three stacked on one another spaced about 18" apart.
Jump standards are easy and inexpensive to make out of a length of 4x4, some 2x4 s for the bottom support and some jump cups. There are lots of patterns
Available online. I have heard of some using 4" PVC pipe for the rails, but I used wood poles instead. I don't think the PVC will stand up in our cold winters.