These questions have been kicked around the board several times recently, and could be found in the archives.......but I'll offer some suggestions cause you been on the board quite a while, and don't post much, which is refreshing.
Price depends on what brand you purchase, Chinabase is cheap for example, but is a crap shoot - maybe works, maybe doesn't, depending on how its been handled. Must be kept cold at all times.
I prefer to stick to the Swiss product - top of the line, doesn't require refrigeration before reconstitution, but not cheap. The Serostim 126iu kit is the way to go. You will probably pay 650. or so for this kit unless you are really well connected, and you need 2 to 3 kits for proper results. Oh, I see it listed for way less, but there are some fakes out there, and I know fellows still waiting after 5 weeks for delivery on a el cheapo offering. I want quality, promptness, and am willing to pay the price.
A good starting dose is 4.5iu a day. You can work that up if you have good reactions to the drug. Some get sore joints, so it's best to work into it.
I always use insulin and a heavy test cycle with the GH for best results. An oral steroid is also a good idea; they trigger IGF release. The GH down-regulates the body's sensitivity to insulin, which is the reason for insulin supplementation.
I doubt the nitrogen build up theory. I have always used prodigous amounts of protein without problem. GH injections cause a rather rapid increase in the system, peaking in about 2 hours, and then falling off rather quickly, so if you are concerned about this, back off the protein for just that period of time.
Injection locations are around the waist and ab area. Subcutaneous, not in the muscle. This site technique will also shrink any residual fat deposits around the injection area - like love handles. GH causes atrophy of adipose tissue - fat - in the site of injection.
I am an older guy, so GH is very effective for me. I have many years of personal experience, have tried them all, and I think this is everything you asked about.
Oh, diet........eat clean, and eat a lot, unless your primary goal here is to get extra lean. Gh shreds me no matter what I eat.