HELP Dog has Lump/Tumor on side of leg Worried

hello guys I am so worried, my dog has a lump on his left leg, near the inner side of the leg, more towards thecenter bone but not exactly on the bone,

when i was touching is leg I noticed that lump, but the lump moves when i touch it? I am so worried and not sure what to do, because right now I have no money for the vet, anyway advise on what that could be? please help as I am soo worriied and thinking the worst my dog is 8 yrs old, i will try to get him to teh vet this month some time when I have more money I feel so guilty about being broke now that my dog needs vet care :( but hopefully this is not a disease that can spread, he is acting pretty normal.