You know, it's very speculative to assume that your dog could have been bred. What championships has she attained? To warn you, just to breed, for breeding's sake, you will find, will not get a favorable response on here. Has your bitch been health-tested? (not just vet-approved) for heart, thyroid, hips, etc.? Have you gotten a breeder-mentor to help you pick the right sire and guide you through this process? Do you have an experienced, opinion (other than your own) that your bitch is an excellent example of the Boxer and should be passing on her DNA to future generations? Otherwise, she should not be bred.
There is no guarantee your dog would have successfully whelped a litter, and if so, the number of puppies. And per ABC code of ethics, no bitch should have more than three litters during her lifetime and not ever after the age of 6.
I think you will have a hard time proving your "profits" plus you have to subtract stud fee, health testing costs, costs of raising the puppies, vet fees for exams and possible caesarian birth. Many times, puppies die, or the bitch herself may even die in whelp. There may never have been any puppies at all. Just my opinion, but your dog will be healthier and live longer now that she is spayed. BYBs and inexperienced breeders are not condoned here. If you are willing to learn, welcome. If you are just going to be angry after reading the posts here, well, take that for what it's worth.