lowering cost basis

The short answer is "yes." Are you trying to do a buy vs. rent analysis? If so, the following is a good tool. If not, perhaps someone else will find this info helpful. I came across this on other threads on SE.

http://www.nytimes.com/2007/04/10/business/2007_BUYRENT_GRAPHIC.html

You'll most likely need to update the Advanced Settings (Rent, Buying, General) to get a better estimate. With that said, the "Annual home price appreciation" is a major factor and probably least predictable at the moment. i.e. a 10% drop in the next couple of years will throw the calculations off by quite a bit with a 5 year horizon.

You might also want to click on the "Methodology" link for more details about how they did the calculation.