They don't look too hard to make! Is time an issue? I'm sure you could build better yourself easy!
Bluntly put, the Antonicity ones look dead simple.
Get a suitable sized strip of wood from the hardware store and cut blocks off it as the base.
Cut a slightly smaller piece of cardboard (thickness to taste) for the mattress and wrap some tissue around it for the sheets. Soak with white glue.
Add pillows and accessories to taste.
Anyway, that's how I'd do it.
If you want the sheets to go over the sides, it's even simpler.