I want to connect the Generator output with rectifier by using solid state switches instead of contactors
its 1000V 100A output

Is it possible to get such solid state relays or switches?
will it cost less than mechanical contactor?

 

While this is technically feasible, the logistics and cost of such tend to be prohibitive. For safety considerations, a mechanical switch or contactor is a far safer solution.

IGBTs require heatsinks
Requires (3) dual packs for 3 phase
Requires isolated gate drive circuitry

Check out Powerex for high voltage IGBT devices--they go up to 6.5kV (for a price)
http://www.pwrx.com/summary/IGBT/IGBT.aspx