There are overnight trains running to Crimea from throughout the Ukraine. The cost will vary based upon where you will be leaving from, but from the Slovak border to cost is about 20 USD in the third class, 30 USD in the second class.
If you travel by overnight sleeper train it is quite comfortable, cheap and the quality is OK. Just the average travelling speed of trains is slow in Ukraine in general about 90km per hour.
There are flights to Simferopol from Kyiv, Lviv, Moscow, Istanbul, and many western European cities, including Frankfurt, Tallinn and Riga.
There is a Euroclub-bus (http://eclubreisen.de) from various destinations in Germany to Simferopol.