/ FEL #11  
Around here, on a loader for a compact tractor (25 to 50HP), base price is around €2950 (fully mounted on the tractor and ready to go). It's around €300 more for mechanical self leveling or €400 more hydraulic self leveling. Honestly, it's worth the slight more investment.
   / FEL #12  
I don't disagree, but that's a commercially-designed linkage that isn't built twice as strong but half as smart by a DIY'er. I feel like there's a lot of room for error that could easily make it a wash whether it was worth the effort to build it. Just my .02.