Buy some free weights appropriate for your strength and some resistance bands. Literally all you need for something like P90X, which will chew you up and shit you out ... but it works! You can do all this from home. Remember that these are the exact tools that Marines use out in the field to keep in shape. I've seen Marines picking up sandbags and doing pull-ups in doorways on deployments. Unless you have a trainer working with you (or you go to socialize), paying for a gym is a waste of money.