Your answer is $2,000 per ton of cooling you are having installed.
This is simply the cost going rate cost in DC for materials and labor to replace your central air, no duct work or ancillary work included.
And you should always be getting 3 bids. If you don’t really know what you are doing, get the first, then use their scope of work to bid the other two. That way you get 3 apples to apples comparisons.