Lido:
It appears you are a pre-med planning on entering med school next fall. This means that you will be starting as an attending pedi heme/onc in about 11 years from now. No one can begin to guess what salaries will be like then, how debt will be handled, etc.
However, since you really want CURRENT numbers, all pediatric specialties are on the lower side of the pay scale and not necessarily much higher than non-specialty trained pediatrics. For academics, it is typical for starting salaries to be between $100-150,000 although some can be higher or lower depending on location and specialty. I don't know specific to heme/onc but I believe it to be probably mid-range in there, possibly on the lower side, certainly not on the highest side. Those fields in which private practice is a meaningful possibility (e.g. neo, but not ID) may have the opportunity to make a good bit more. I don't think that is too widespread in heme/onc, but there probably are some chances to start higher somewhere in the US in private settings or a few academic ones. As far as mid-career numbers, you're asking for us to look over 20 years into the future. No one can do that in any meaningful way.
Now, heme/onc is a heavy research field and many who go into it are doing research and will apply for the NIH grant repayment program. Again, guessing what that will look like a decade into the future is impossible.
Bottom line is that if you are going to graduate with a very large debt, the extra 3 years of fellowship training will add more debt and be a challenge to repay, one potentially made easier via the NIH loan repayment program if you are a researcher or via private practice in limited settings. Only you can decide if it is worth it - there are endless threads on SDN regularly about the issues of loan repayments and lifestyle that don't need to be repeated here.
One final point: There is no such field as pediatric oncology. It is pediatric hematology/oncology. You WILL spend a good bit of time in training and likely afterwards doing hematology.
