Help my guinea pig looks very sick!?

shes a female and she has some brown stuff all over her nose it looks like its giving her breathing trouble she keeps couughing and shakeing she is kind of oldi guess i have had her for about 3 years so she is about 5 years old. i dont know what to do for her. i wnat to do somthing i cant take her to the vet right now i dont have the extra money. but is thier somting that ican buy for her thats under 50 bucks? im really worried. plz help. if you no of a website were you can ask vets questions for free plz let me no.