Only UA miles allow for one-way awards. US does not do one-way for half-price of an RT. You will pay the RT price even if you book one-way with US miles.
Also, to qualify for the off-peak awards with US, you must fly US metal. US does not fly to CID or UIO, so you cannot use the 35,000 rate for that.
I also wouldn't waste hotels -> airline points, especially since you have time to accumulate points easier. Can you apply for cards in the near future? Do you have a US Airways MC from Barclay's or the UA Explorer Visa from Chase? Both have bonuses after first purchase (40K US, 50K UA).
What class of service are you looking at? And what other airports can you fly out of besides CID?