Despite the decrease in costs, land will still be limited, particularly in prime real estate locations. While construction may be cheap, the scarcity of land in desirable locations will make these properties highly sought after.
As a thought experiment, suppose we developed a method of transit that enabled you to go between any two locations in the US within 30 mins. I think in this case, real estate prices become more uniform.
If you exclude land near "natural wonders" like Yosemite, prime real estate is prime because of its travel-time proximity to other people. For example, NYC is expensive because you're close to cultural production. If we had a way to get to downtown Manhattan from Sedona, AZ, prices in Sedona would become about equal to those in Manhattan.
The upshot is we don't know what the future prime real estate locations will be. If we enter an era of rapid technological progress and decreasing energy costs, transit will become both faster and less expensive but the exact form of it isn't clear, so we don't know which areas will end up being "linked" or whether the transit developments will apply uniformly to all land.
This is the way the world ends: not with a bang but a waifu