How is he this morning?
Home treatments could help to a point but I have to agree, this pig does need a vet. Sudafed Expectorant, 0.2ml 2x daily may help to some small degree, as well as allowing the pig to sniff some Vicks Vaporub/Olbas Oil - but really, these will not fix him, they may just buy him a little time. From the symptoms you describe I would have the pig on antibiotics at least.
Maybe worth looking over this thread, don't take it personally, but it should put something into perspective with regards to who may be actually responsible for this guinea pig:
http://www.theguineapigforum.co.uk/showthread.php?t=36801
People won't drop the pleas to get your pig to the vet because there are times when it just has to be done. Depending on where you are, it may even be illegal to deny your pig medical treatment when it is clearly needed (as it is here).
I lost a guinea pig, very dear to my heart, less than two weeks ago. His only symptoms were weight loss, a snotty nose, watery eyes (for one day only) and not eating. He didn't even have the crackly breathing you describe, yet it was clear he had an Upper Respiratory Infection (URI). He was started on antibiotics (as well as being syringe fed, with him not eating) but I suspect the antibiotics were given at too low a dose; he passed away five days after symptoms started. URIs, when distinguished from other causes of the symptoms, are not something to take lightly. Untreated URIs will spread further down the respiratory tract, turning the condition into a lower respiratory infection i.e. pneumonia/"chest infection" - and you really don't want to have to try to have your pig recover from that. I have had a pig with pneumonia as well and can safely say, hand on heart, it was one of the hardest conditions I have had to get a pig through.
Whereabouts are you? Perhaps we know of a good vet in your area who charges less for a consultation than the one you see.