If a breast lift patient needs or requests implants to further enlarge breast volume, the answer is easy: lifting AND enlarging the breasts involves more incisions, more "inside-the-breast" surgical dissection, and much more surgical closure, all of which take more time and skill than Implant placement alone. Breast augmentation requires only a small incision, precise creation of a pocket for the implants, insertion of implants, and rapid closure. Cost of any operation is related to both the time and surgical effort/skill required, not to mention operating room time, anesthesia time, and the related increased costs for these things as well.
Even in a breast lift that requires no implants, the longer and more detailed planning, incisions, and surgical closure are attended by increased costs. Much more judgement, artistry, and experience is required for excellent outcomes with breast lifts!
Also, there are different kinds of breast lifts, and each of these will have different costs based on the individual details of each kind of lift. I hope this helps!