You want to build second floor (or more) deck without a house to add support. So lets say a 10x10 platform, 12 feet off the ground, one set of stairs and you said "I don't wanna dump a whole lot of money into it but still want it tO be real sturdy". I see a Darwinian twist to this.
For a correct installation you are looking at 4x6 PT post set on footings, not holes filled with concrete. You will need cross bracing. Your deck surface will need to be at least 5/4. You will need a railing for stairs and the deck. You could greatly enhance the stability if you could plan this platform between two trees. If you are not familiar with construction you may not realize how quickly this bill is going to add up. I have no problem building something on the cheap, like a firewood rack. But when you are building elevated platforms, or any structure which will be above people you need to take a bit more care. Try googleing "deck collapse Chicago".
I know that in my area this would quickly catch the attention of the building department. I am not Capt. Cautious, but please use common sense. Any time I build a deck I ask myself -- What can I do to prevent a 300 pound party guest, who is half in the bag, from hitting the ground without using the stairs.
Before you embark on the project take a look around, any sections of flat roof to use (shed , garage), hay loft with a door, second floor window on the back of the house, etc.