I would store it at your buddy's place. You don't NEED to have the car within 5 minutes of you at all times, it's just more convenient. You also don't NEED to work on the car, it's just fun to do so, since I'm assuming it's not your DD. Doesn't sound like it is. IMO, the extra charge for a place with a garage sounds like a luxury fee in this case just to keep your Z close.