Definitely do it for $350 if the guy is legit and has trained winners before.
Having someone TELL you what to eat is extremely helpful instead of trying to figure it all out on your own. You don't have to worry about anything, he just tells you what/how much to eat and you just ask him if you're not sure about anything. Much easier than doing it on your own and wondering all the time.
The training is going to be somewhat important as well. There are many different schools of thought. Some people think you need to train heavy as you get close so that you preserve muscle. Others think you need to increase reps to help bring out the muscle more and control your body.
The posing though, that will be INVALUABLE. Go to a local show and you'll see tons of people who have no idea what they are doing. They just get up on stage and flex their muscles, thinking that's enough. Shit, on this board go the Rate My Physique forum and look at how poorly people pose. Then they get lower ratings, not because their physiques aren't any good, but because they don't know how to show them off. Your guy should teach you all the mandatory poses and all the relaxed poses, how to move your feet, how to breathe properly so you don't shake, how to smile instead of looking like you're taking a dump, etc...