I’ve had bunnies with odd lumps before. Bailey had a strange lump on her ear that was never fully figured out (returned even after it was surgically removed). Jack has some fatty (old age lumps) but they are not cancerous and do not inhibit movement or cause problems. But in each case, I had these lumps checked, because really…there’s no way to no what is harmless and what isn’t. Vet can be pricey, but you are paying for their expertise. I think the important part —- and money-saving aspect, is to find a rabbit-savvy vet so you don’t have to go through treatment after treatment, test after test. (though that can still happen with rabbit-savvy vets too – it’s just that at least you know you are getting the right treatment and not wasting money)
Do you have a vet you trust with rabbits? rabbits are actually considered exotic because of they way they react to certain treatments and procedures and most vets actually have to get extra training for this. (which is why they can be a bit more expensive)
Anyway, if you have a rabbit-savvy vet— Yeah! If not, maybe we can help you find one.