red lump on syrian's belly but behaving as usual

[gorou]

hello, this is my first post so i hope i am doing things right.

my Syrian hamster is named Dio and i got him from a pet store which i know is not the greatest but not my choice, unsure of his age though he seems young. ive had him for almost a year. he's been doing fine, he is still wary of me and because of the holidays i just now found this red round lump on his underside, other than that he behaves as he does and acts healthy.

any help identifying the problem and cause and maybe what to do? also maybe projection of cost, i want to make sure i am prepared for all of it.

sorry for any difficulties i am autistic and very emotional over this i do not want him to die.

for any extra context he is in a large bin cage, has a wheel and whatnot and eats science selective hamster food