The World Bank lists Russia at $14,037 per capita income.
That same source lists Ukraine at $3,867.
Russian per capita income is slightly more than 3.6 times higher. I am not suggesting that Crimea will now experience an economic boom, but this differential is worth keeping in mind as the issue unfolds.
Admittedly the Russian incomes are distributed quite inequitably (Gini of 40 compared to 26 for Ukraine), which lowers the attraction of belonging to that country.