Zep said:
Stalin cared not a whit for the cost of anything to do with the war, least of which were the finances.
The political tensions run very high in Europe in late 1939. Starting the war against Finland incurred a risk that Soviet Union would be drawn into the war between Western allies and Germany. And that wouldn't have been similar triffle that Stalin believed Finland would be. Doing the things peacefully would have lowered that risk.
And the war between SU and Western Allies might have come to pass. The leaders of UK and France offered to send official military help expeditions to Finland if the Finnish government asked for it.
The offer was declined, mainly because Finnish leaders realised that the Western allies wouldn't be able to send strong enough forces to stop the Red Army at the same time when they prepared for the expected German attack.
And the British archival sources have confirmed this viewpoint: the operation plans for the relief expedition concentrate on how to seize the Swedish mines to prevent the Germans from acquiring Swedish iron.
The Soviet high command actually believed that there already were British fighter squadrons operating in the Karelian Isthmus at the end of the war. At the Red Army crisis meeting in April, 1940 several participants claimed that the Red Air Force had shot down a couple of British Spitfires that were flying in British colours. Those claims were mistaken.
And the usual method of covering up military, or indeed ANY, embarrassing reverses was to simply expunge them from history and/or proclaim them victories instead.
I once managed to find the complete History of the Great Patriotic War, all six thick volumes published by the Marxist-Leninist Institute of the Central Committee of the Communist Party from an old books store. I bought it immediately, of course, even though my Russian is very, very bad.
Naturally, the book concentrates on the Eastern Front in 1941-45 but it gives also short accounts of war events in all other fronts. Except that I couldn't find any mention to Winter War at all. Or more precicely, it may have been mentioned in some part of the text that I don't understand, but there certainly are neither pictures, maps, nor captions that mention it.