It sounds like I am being harsh on your parents. I am sorry.
The fact that we all care deeply about is that your guinea pig is just not likely to have a good outcome at all without immediate vet attention, and we mean immediate. I don't know how old you are, but you are obviously mature and caring enough to come here for help, and I feel you care deeply about your guinea pig. You are in an upsetting situation and hearing that your guinea pig is likely to not make it without seeing a vet is a horrible thing to hear, but I don't believe in pretending that things are going to be OK when they are not likely to be, it would do no good.
The other sad fact is that out of hours emergency vet care is expensive, and your parents have the responsibility of running a household, affording all of the extras, and sometimes it is really hard on finances.
We do have strong feelings because most of us here would find a way, somehow, but ultimately it is your parents that face a dilemma between taking a pig for emergency treatment and their finances.
We all know what's best for your guinea pig. None of us know what is best for your family. Please let them know your pig is likely not to get better without the vet, but please don't be resentful at them if they do not make that decision. Wishing the best of luck x