I'm afraid you simply cannot get a hobby grade RC car (one that will go at any speed, be wrenchable and upgradable) for $100. You're looking at $250 for the cheapest car worth having, but that would be an RTR, including everything you need, radio, engine, etc. I see you've been searching on ebay, so you are not averse to second hand? I'm afraid once again, that second hand RC cars are highly NOT recommended for beginners. the best thing you could do is go to a local shop that deals with these things and talk to the person behind the counter. I too love the 350Z, this hobby is very rewarding, but it's not cheap by any stretch of the imagination. Especially nitro. Imagine...I'm about to spend over 1000 euros on a new kit and engine, and I already have a $400 radio and many other things. Ok, that is another extreme, but you get my point. I strongly suggest that you do take the plunge into this hobby especially as a car lover, but even more strongly, I suggest you buy a new one from a local establishment, where you can get spare parts, and most importantly support in the early days. Second hand cars are normally thrashed to pieces or out of date, that's why they're being sold. You'll need to change, repair and otherwise maintain something which is very new to you. Don't buy someone else's problem, create some of your own.

EDIT: Also, on most of the touring cars, no, there is no need to cut the shell for the engine head (it's the cooling head of the engine that you can see, and I'm afraid it is absolutely necessary that it is the size it is), they normally sit just below. Many .12 size engines have small cooling heads anyway, it might be something to worry about if later on, you wanted to put a high power .18 engine in. You WILL however, need to cut a large hole in the windshield, and many smaller holes in the rear windshield. This is necessary for cooling on nitro models, but can easily be done in a 'pretty' way.