The price range of the synthesizer for a beginner varies from five to fifteen thousand. More expensive tools are not worth buying: the production technology constantly updated, technology is constantly falling in price. A synth for a beginner, by definition, will not serve you for a long time: eventually, a musician will "grow" out of it, you will need to buy new, more expensive and functional, and the old market, of course, at a lower price.
The number of keys on a keyboard varies from 39 to 88 respectively, from three to seven octaves). At the initial stage it is better to choose patientally tool: a larger range is not needed (pieces are not so complex), and the smaller of them may not be enough.
Feel the keys themselves. Ideally, they should be tough, resilient, like a real piano. To do this, before going to the store better to feel the keyboard of an acoustic piano.
The abundance of melodic and rhythmic samples at the initial stage does not play a role. You can choose a synth with a small set of sounds, and later to replace it.
When going to the store, invite an experienced musician friend of a friend, relative, or another keyboardist for the band. Bit cheaper to pay him for assistance in tool selection, than to suffer the results of wrong choices.