Hidden costs?
With Tirerack, there are none. Calculate shipping, and you are done, unless you also want locking lugs. Balance, "Road Force" analysis, standard mounting hardware, valve stems, are all included, and they stand behind their work.
With Discount Tire, be wary of so-called "free shipping." When they went to "free shipping," all of their prices went up. If you compare, say Kumho 712's from Tirerack, to the same tire at DTD, it's still cheaper to your door from Tirerack. Furthermore, they will charge you for the mounting hardware, whether you need it or not, and even for the valve stems, which I could have sworn were part of the hardware? And as you've already seen, the road force analysis is another $40. In that case, I would wait to see if you need it, and then have it done locally.
There are some really good prices now at TR for 16" wheels that are attractive, and not too heavy (like around the 19 lb range). 16's will look fine with your stock ride height, but 17's start to look lifted unless you lower it.
If you really don't like the wheel selection at TR, then go with DTD, Whalen Tire, or some other places recommended here. But I would seriously consider the vendor as a factor in your ultimate choice, with the chance to buy from TR a big plus, in my book. (and no, I don't work for them :p )
