$1900 for a 600 square foot driveway doesn't sound all that bad. A 600 square foot drive translates to one that is 16 foot wide, 40 foot long. I am assuming the contractor is going to dig or grade out the existing dirt drive, fill in with a minimum of 6 inches of gravel, then add a minimum of 4 inches of concrete. (some will say 6 inches is the minimum you should go with)
A rule of thumb for paver bricks is that the cost of doing that yourself was about the same as having a concrete drive put in.
Have you had at least 3 - 4 competitive quotes?