The race to the moon was indeed highly political. Spending a similar amount of GDP is not currently feasible, but that can change in the future. You only had to listen to some of the themes from the recent Presidential Elections to see that China looms large on the political landscape.
As far as propulsion goes, landing on Mars and then returning is indeed a tall order with current rocket tech. Creating extraterrestrial fuel sources (e.g. on the moon, or boosting it up to an orbiting refuelling rig) would help due to the advantage of not having the rocket drag it up the gravity well of Earth. Cost is obviously the reason this hasn't happened yet. Political will or much more advanced technology are both solutions, but neither are happening in the next 5-10years.
As far as muscle goes on space journeys; using weights in a weightless environment is counter-productive. What you can do instead is use resistance training. Imagine a thick rubber band and pulling that apart. This is currently in use on space station.
Hope this helps!