Appendicitis pain will most typically emanate from the lower right quandrant around the belly button, not the upper. The area you're describing is the upper right quadrant, which is where you'll find the liver. Pain in this area can stem from a number of things which can be as minor as referred intestinal pain from gas or a virus, a cramp (common in this region and generall occurs when carbon dioxide levels become slightly out of balance, usually because of exercise), a mild hepatitis (liver inflammation) which can arise from main types of insignificant or serious viral infections, something going on in the lower lobe of the right lung (a potentially long list here), a mild injury to the area, etc. In otherwords, there are a lot of differentials, and you need a qualified medical professional to sort them out -- not a bunch of untrained moms who can only offer anecdotal advice.
As always, the best place to go for medical advice is to a doctor. I understand the problems of not having insurance, but you can't ask for a diagnosis from a bunch on nonmedical professions, nor could you ask a medical professional for a diagnosis who is not given the opportunity to see your child first hand. (I swear, I'm starting to sound like a broken record on this matter!) Signs and symptoms that can help you assess the severity of your child's condition and decide if it's necessary to to see a doctor include the following (individually, not necessarily occuring together):
Your child's pain is increasing
He's vomiting or having diarrhea and losing lots of fluid over a short amount of time
He's become very lethargic
He's running a high fever (over 103 for a couple of days)
He seems to have entered an altered mental state
He's become nonresponsive
He begins to look jaundiced (yellow staining that will show up first in the whites of the eyes and oral mucosa of the gums, then spread to the skin).
If If any of these arise, take him to see a doctor immediately. If you don't want to wait, consider taking your son to an urgent care facility rather than the emergency room. The cost is usually a lot less, and you'll be seen in the order in which you registered, rather than triaged by serverity as you would be in the ER.
Also, check with the state of Nevada Health and Human Services. Some states offer no- or low-cost insurance for all children.
I hope your son feels better soon!