Frequent sneezing is always something to keep a very close eye on. Try putting your little ones chest up to your ear, listen for signs of gurgling,wheezing or wetness. If you hear any of those noises, its best to get the piggy to the vet ASAP.
Make sure to check these links, they offer great information on sickeness, signs, normal behaviors, dangerous antibiotics and probiotics:
Information about upper respiratory infections:
http://www.guinealynx.info/uri.html
Dangerous medications:
http://www.guinealynx.info/dangerous_medications.html
General medication info:
http://www.guinealynx.info/medications.html
What is normal and what is not:
http://www.guinealynx.info/normal.html
Probiotic information:
http://www.guinealynx.info/probiotics.html
Also, if youre concerned, the best thing to do is take him to the vet and also weigh him on a daily basis to make sure he isnt losing weight. This is a very good way to determine if your piggy is sick. Weight loss is a warning sign of sickness and if a sickness is not treated
before very noticable signs develop, it could be too late.
I cant really say what an average vet bill is since Ive only had to take my little guy for a wellness exam (thank goodness), but if a piggy is sick I would like to estimate the cost for medication and the appointment would be about 150-200 dollars. Its very hard for me to say since the vet I go to charges 50 dollars just for an exam. He is one of the best exotic vets in my area and also owns his own piggies.