The $2500 is a collector's edition of some sort. The normal Sebenza's run about $400, and comprise the standard for quality folding knives.
Blades are like anything else; quality will only be distinguished by holding different knives and by what job you intend them for. If you rarely pull the knife out, a $15 Mora will do you just fine. If you carry and use a knife every day, why short yourself? What's a extra couple hundred dollars, in the long run? Better blades will have better construction, materials, steel, balance, grind, and ergonomics. Better folders will have tighter tolerances.