How do you know for sure your piggy has a respiratory infection, sounds like you've not been to a vet?
The costs others have said sound about right, but as you can see there is a little variance so I suggest you call round any vets you might realistically be able to get to and ask them for their small animal/exotic prices. They should be able to give you a consultation price, though may not be able to tell you treatment pricing without knowing the specific treatment your piggy needs.
Hope this thread has helped with planning a vet appointment, good luck