In many cases, revisionary breast surgery is significantly more involved and requires more surgeon, anesthesia provider, and surgery facility time, compared to first-time breast augmentation surgery. Also, sometimes revisionary breast surgery does involve the use of additional "materials" (such as acellular dermal matrix, for example), which involves additional expenses. I hope this helps.
With the exception of very simple implant exchanges revision breast surgery tends to be a lot more technically challenging and takes longer which translate into higher costs. Sometimes expensive products, like alloderm, are needed to correct certain problems with and those cost more and add surgical time as well. Finally, primary breast augmentations can be relatively inexpensive because of various sales or promotions offering discounts. Revision breast surgery is much more specific to each patient so it is priced individually and generally reflects the true cost of surgery.