I had thought about getting a biocube. They look nice and everything's in it already (except a skimmer). You said that $ is an issue. They are not cheap, and if anything breaks down, you have to get parts designed for the nanocube that run pretty pricey in comparison.
After researching numerous possibilities, I went with a 20
gal high, and bought all the individual pieces. The only thing I regret, is not getting the 29. I bought a 5
gal hex with built in parts, and because of that experience, I will probably always go with the build your own set-up. I like being able to pick and choose my filtration, light wattage etc....
The other issues seem to be weight and space. Are you in a dorm? I don't think a desk is the best option for anything over 8-10
gal. Especially
SW, because I'm assuming you're going to be sticking
LR in there, plus sand, plus water weight. With a 10
gal tank, you're looking at about 150 lbs. Depending on what kind of desk it is (wood, plastic, filler board), it could end up in disaster. If it's one of the older desks that are made pretty sturdy, I would suggest spreading the weight out as much as you can. Maybe a 15gal or a 20 long would work, that is, if the desk is built extrememly sturdy out of solid wood.
That's my input.
HTH