Why is my cat drooling out of no where?

So my cat is very old she is around 11 now. I had her for about 2 years but she been in the family since she was a baby. So I woke up and she was sleeping on me (which is a normal thing she does) and she had a big drool spot fom her mouth it look like she just woke up with me lol. Anyways I wipe it and all of a sudden it came back and I just keep cleaning it and it keeps happening. So now I'm worried. I been reading up on google to find out things like if it smells means its bad. It doesn't smell and her mouth doesn't smell also so I don't think its anything to do with her teeth. So can someone please help me? And I don't have money for the vet cause they charge an arm and a leg to say this is normal. I just need someones option.