Apparently the directors of Skyline were working on Battle Los Angeles and in their off-time, started work on Skyline, borrowing everything from resources to equipment to make the money which is probably why it cost so little to produce.
They got sued, of course and eventually reached an agreement. Doubt a sequel is in the works.

I looked at the FAQ's - apparently, it cost 500,000 to shoot and 10,000,000 was spent on the digitals.
I watched it again last night (it was broadcast) and realised the problem. Lack of dialogue. Questions and panic/fast speaking would happen to most people but they hardly spoke. It was slightly frustrating.

while the effects are a bit ropey in areas, for $10 million no one can argue that they are great
I would have expected maybe $40-$50 million