I can sort of see a horizontally across, about the pink area. Is that what you meant by a dent? Try get a closer look as it may be a bite mark from the other rabbit. One of my rabbits got a bite there and has a bit of hard scar tissue there now.
Bites and other wounds can become abscessed quite quickly. Dealing with abscesses in rabbits is no fun. The pus cannot be lanced out with a needle because it is too thick.
I would do some investigation online and see if you have vet clinics that will do payment plans so your parents won’t be up for the full fee all at once. It is worth looking in something like care credit also. http://www.carecredit.com/vetmed/
You might like to take a look at the links on this page also, listed under the sub-heading “vet care and financial trouble?” https://binkybunny.com/RESOURCES/tabid/67/Default.aspx
Hopefully there is a solution to be found for when money is tight.
In the meantime, it wouldn’t hurt to put some plain neosporin on this, although how much stays there will be the challenge! Just take care
not to use any type that has added pain relief.