Especially with scars that are thick and raised (hypertrophic) or extend beyond the normal scar boundaries (keloids), scar "removal" is not always easy or even successful, regardless of surgeon or technique used, including laser. This is even more problematic for darker skin types, and also for the knee areas, which heal poorly in many individuals because of the constant motion of the knee joint.
Lasers do NOT provide any better excision technical advantage over a sharp surgical scalpel; in fact, lasers used to make incisions can actually create more scar tissue because of the "burn" (thermal injury from the intense laser energy) at the edges of the incision. Cold steel scalpels don't have this burn injury component. Excising keloids often lead to even larger keloids than the original!
Lasers used for resurfacing will still leave the keloid base and a new freshly wounded surface, which can heal as bad, or worse, than the original scar.
What you really need is a consultation with an experienced, board-certified (American Board of Plastic Surgery) plastic surgeon. If he or she is experienced in laser technology, then you can ask questions about this as well. Cost estimate will depend on the extent and size of the scarring, and the technique and time used; your consultation will answer this question as well. This could cost as much as several thousand dollars, or your consultant may recommend no surgery at all..