That's a little like asking what a car costs. Depends on the quality.
Around here round bales of far quality grass (~1000lbs) go for $15-25.
Small squares (50-60 lbs) go for about $2.
This stuff is mostly fescue/clover or bermuda.
High quality stuff will cost far more.
In a city who knows what people will pay. I have heard of much higher prices 2x + on the east coast for small squares.
Fred