From your 2x4s, cut for each horse:

• 1 top beam at 36"
• 4 legs at 30", with a 15° angle on both ends (angles parallel, like a parallelogram)

Set your saw to 15° once and cut all eight legs in a batch so they match.

Stand the beam on edge. Hold a leg against its side, flush with the top and splayed outward, and drive three 2 1/2" screws through the leg into the beam. Glue first if you want them to last decades. Repeat for all four legs — two per side, mirrored.

Cut four scrap pieces of 2x4 roughly 12" long with 15° ends. Screw one across each pair of legs about halfway down. This stops the legs from racking and doubles as a shelf for clamps.

Set each horse on a flat surface and check for rocking. If a leg is proud, mark it against the floor and trim the bottom with your saw. A sawhorse that rocks is a sawhorse you'll hate.

Repeat everything. Cutting parts for both horses at the same time (step 1) makes this fast — assembly is under 20 minutes once the parts exist.