remember to do some maths before you go shopping and estimate weights into the equations to get a rough idea of power needed so you can find relevant engines. I've done some pondering this morning while I was driving and came to some conclusions based on some rough math. For the current size and my estimated weight, plus size of components; if you really want to use these materials it will probably need to be a lot bigger than 3ft to house all the gear needed just to hover.
Another idea but again it'll need to be made bigger to accommodate for it, is to have a helium filled sack inside the craft to add buoyancy and counter act the weight issue, it won't get it off the ground but it will help.
Look for RC car nitro engines, they should have the power you need, i'd hope. Draw back is they drink fuel! and a lot of it.
you'll need fair sized propellers on the end of the prop shafts to turn that power into lift again another reason for this probably needing to be bigger.
I know you say you don't like foam but it would definitely serve as a better weight saving alternative.
Will be interested to see how your shopping trip goes, keep us posted