1) It's not a matter of cost, it's a matter of time. It takes months to get a new trademark, and Zenimax DOES care about time. If it expires there will be a period of many months in which they cannot announce the game because they have no trademark.
2) If that was how they thought then it makes no sense to have renewed it in January. If they were going to let it expire and then start a new one, why wait until July to let it expire? It's going to take months to get a new one, so why not start early in January?
The only reasonable alternative explanation, that I can surmise, would be to throw us off. Interestingly, Hunted showed up in the trademark records shortly before it was announced. It's a possibility, but I don't see it as a probability.
On another note, we're going to see the next Game Informer cover within a week (most likely) so why not just wait it out for a few days?
You will likely be disappointed. Bethesda have never announced via a magazine, and have always announced first on their website.