My 200 lbs of sand fits into 2 army surplus duffel bags, which can be stacked on top of each other in the corner of a room. Bench, bar, plates, plate storage rack (I have all that too) take up considerably more room.
Overhead presses will do nearly as much if not as much for you as presses lying flat on your back. If you also have the capability to hang a
pullup bar and some rings you have just added pullups, dips, muscle-ups, and ring pushups (there's your chest work), and it's a heck of a lot cheaper. You're talking about a brief period of time, and you want the most bang for your buck...sandbags, pullup bar, and homemade rings should come in around $50 maximum, less by far if you live close to the beach. (I don't know what that is in pounds and I'm too lazy to figure it out.)
A
workout routine using what I have laid out will keep you in plenty good shape for the 3 months you're gymless. Afterwards you may even decide to keep saving your money and continue to stay away from the gym.