Necessity is the mother of invention! Do you want just a stand, or a cradle as well? Are you just wanting it for one horse or a range of sizes? For just a one horse stand, you could get by with 3-4 steel rods, bent into 'L' shapes to make a tripod - weld them together if you're able. If you don't weld, it won't be quite so sturdy, but bolted together with pipe clips or some such.
If you want a cradle too, esp if you want something that you can adjust height for different horses, go to your local auto supplies & buy a couple of axle stands. They'll still cost you more than some steel, but if you have a friend that wants one, you can halve the price & go one each. Get some firm but not brittle plastic, such as thick poly, to extend the cradle bit of the top, add some thick closed cell foam &/or some old carpet over it, to make a supportive but soft cradle.