Strategypage notes that Russia's main threat to Ukraine is natural gas exports:
Russia’s aggression against Ukraine is often described in military terms. That is not accurate because Russia knows that it has a far more potent weapon to use against Ukraine. It’s not what military forces Russia might send into Ukraine that is a threat, it’s what Russia is threatening not to send. Or, as the old saying goes; follow the money. Ukraine is broke, actually it is worse than broke. This is at the heart of the Ukrainian crises.
Russia's actions while Yanukovich was president can accurately be described as a money attack, but since then the military has been used because the money attack was enough to pressure Yanukovich but not enough to deter the people from resisting what their president chose and defeating him.
Russia may not have occupied Crimea yet, with this subliminal war, but the Russians are poised to do so by fanning out from Sevastopol and Kerch to reach all those pro-Russian militias (bolstered by "ghost" special forces and mercenary troops from Russia without insignia) that give the illusion of direct Russian control.
If Russia doesn't want to risk exposing their military as inadequate if there is resistance in Crimea and fighting spreads to eastern Ukraine, despite Russia's boasting of martial prowess; if Russia wants to rely on the energy and money weapons to eventually draw Ukraine into their orbit while holding Western Europe at bay; and if Russia is really only concerned in the short run about losing their Sevastopol base; could we make this a crisis over Sevastopol, as I suggested?
If we arrange for Ukraine to sell Sevastopol to Russia in exchange for Russia supplying gas, evacuating their crisis-level troops from Crimea, and abandoning the pro-Russian militias (with amnesties), could we end this crisis without Ukraine losing anything it hadn't already lost (Russia does have a long-term lease at Sevastopol)?
Heck, Russia could simply accept the Sevastopol request for annexation while rejecting Crimea's expected request after Sunday's referendum, getting a little propaganda boost.
We'd make the Ukraine crisis a low-key, long-term economic and political struggle rather than this immediate militarized crisis that will result in military responses in at least a short-term Coldish War environment?