How much do cracked MacBook Air screens usually cost to replace?

There is no 2000 MacBook Air model. The first MacBook Airs came out in 2008. Did you mean to say "2010?" If so, Apple considers this model to be "obsolete" repair-wise. That would mean that they no longer carry replacement parts for it. However, you may still find an Apple Authorized Service Provider or use a 3rd-party repair outfit that can help you with this.

If it can be done, expect it to be in the $600US area. Give or take $100US.