we build much larger structures that this all the time here on Earth are capable of withstanding the forces of storms at sea
No we don't. The longest battleship I know of is 333m long and the worlds longest ship is only 460m long [http://en.wikipedia.org/wiki/List_of_world%27s_longest_ships]. These are exceptional, we don't build even these short things these all the time. You are looking for a 500m radius, which means we need something twice that long to make 2 little habitable zones on either end.
battering waves...Something built for space doesn't need to be remotely as rugged as an aircraft carrier.
Hunks of space debris traveling at relativistic speeds may need to be accounted for. Also radiation shielding is not just for humans, it screws up all your electronics too. Plus there are other design You do need to make this proposed space ship pretty durable as well. Also consider that aircraft carriers need regular servicing, so put that in your budget too.
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We built the worlds longest craft ever and armored it for space; let's launch it:
A fully loaded space shuttle is something like 200,000lbs and the launch weight (e.i. fuel + breakaway boosters) is something like 4,500,000lbs, over twenty times the weight of the craft. Launching the shuttle costs about $450,000,000 per mission [http://www.nasa.gov/centers/kennedy/about/information/shuttle_faq.html#10]
The seawise giant (1/2 the length we need) with no cargo is 183,408,960lbs. And assuming I we can magically scale our shuttle-scale launch gear up to that size at no additional cost (we'd probably launch the pieces and asseble it in space, though we don't have the tech to do so yet).: its launch weight will be 4,126,701,600lbs and cost $412,670,160,000 to launch. 400billion, which is actually doable, but that is just for the launch assuming everything goes perfectly and we already have all the equipment sitting around.
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So, yes its technically possible and earth could use fewer religious zealots hating science, but this is alot of work to prevent astronauts from getting dizzy on landing.