There are two grand examples of Scorched Earth policy that I can think of - Napoleon's invasion and WW2. I'll address the events in Napoleon's invasion, and someone else can talk about WW2.

During Napoleon's invasion, the policy utilized by Alexander I was combined with the strategy of funneling the subsequent retreat of French troops along the same route. This means that there wasn't a massive front that swept across Russia where all the crops and population centers were destroyed. Here's a map of the invasion: https://upload.wikimedia.org/wikipedia/commons/0/07/Patriotic_War_of_1812_ENG_map1.svg

And here's a map of the retreat: https://en.wikipedia.org/wiki/File:Patriotic_War_of_1812_ENG_map2.svg

You can see that the advancing French troops left approximately along the same path, and no vast swaths of land were burned or destroyed. This means that the agricultural impact wasn't as great as it would be expected from a large invasion. The French troops were not allowed to forage as much as they normally would, and the heavy casualties that they sustained were due to the fact that they were forced to retreat over already depleted lands.

The Moscow fire, however, was a major economic event. Moscow was obviously a major center, and the reconstruction took a long time. Alexander created the "Commission to Rebuild Moscow" in 1813. According to Balyazin in his "Unofficial History of Russia"(http://books.google.com/books?id=Ks2pauQ5kJMC&pg=PA415), the commission received an interest free loan of 5 Million Rubles. I would love for someone else to do the monetary conversion to today's value, but the Ruble was about 21 grams of 0.8680 pure silver (http://en.numista.com/catalogue/pieces9395.html).

Much of the city was destroyed, and former owners were forced to sell property at steeply discounted values. It's beyond me to estimate the total economic cost of the fire, but judging by the reconstruction loan, the economic impact was massive.