It really depends on the type of music you do . You could get an older analogue YAMAHA CS-50 , CS-60 , or the SK-15,SK-30 . The CS series are polyphonic analogue synths and the SK series are basically string machines with some limited synth and organ controlls as well . If you want something more recent , you might try a YAMAHA SY-22 or SY-35 . The larger more feature packed SY series are exspensive. But mixers in a keyboard is not that typical unless it has something to do with it's sound editing facilities. If it doesn't have to be YAMAHA , you can get an old ROLAND JUNO-6 or JUNO-60 for CHEAP (80s analogue polyphonics ) or a KAWAI K-3 or K-5 are also very nice and feature packed and inexspensive .