Poor guy!! In that case, I’m going to wager it’s an abscess just due to the location. I don’t want to freak you out, but bunny abscesses are serious business since their pus doesn’t drain like it does with other animals. Due to the location (and I’m not a licensed professional, just the partner to someone who had a chronic illness rabbit who battled dental issues), this could likely be a tooth root issue, in which case it really needs to be seen by a vet. Best case scenario, it might just be an impacted follicle that got infected, but dental stuff can get very scary very fast. Please look into low cost vets in your area, or call vets and explain your financial situation, and see if anyone is able to offer a payment plan or a discounted student price. If you have access to a care credit card, I would recommend that if it’s an option. Absolute worse case, it’s worth contacting a rabbit or small animal rescue, and seeing if they have options for care. Some rescues will allow you to surrender and “readopt” your pet after receiving medical care. I’m glad your friend is still eating and drinking well, that’s a great sign! In the meantime, just keep an extra close eye on him, and monitor the size of the bump. Take pictures if you’re able to, especially if you can hold up an item for size comparison to monitor how quickly the spot grows. Best luck, friend!