Speaking as a flooring business owner since 1998, every condo application has always had more work involved: parking issues, storage of materials/tools, limited working hours, extra efforts to keep common areas clean, disposal of trash and dirty water from wet saw, logistics in general. This is the reality and every professional with experience will want to get compensated for their time under these conditions. While every region has its set of prices, the prices you have been quoted are in line. I am however surprised on the low cost of the material. This could ultimately prove to be challenge for the installer. Marble/Stone in this price range is usually of poor quality. Lots of fills with resins or latex makes for a weaker product, not square or inconsistant edges, thickness varies and more importantly the fills do not take sealers.
In Austin, Texas, these prices are right on, except every condo project I have ever worked on required leveling of the slab. Yet, there is no mention of this in your numbers. Unfortunately, every job is unique, so some may require more or less. However most projects of this size will range between $500 - 1200. All natural stone is not easy to work with and requires extra care and a detail oriented crew. As for the sealing, I would want to know what quality of sealer is being used but the price is right on. Assuming they know how to apply it to manufacuture's specifications.
Perhaps, you can save money by transporting the material and/or doing the sealing on your own. Be prepared to carry over 6000 pounds and have sore bones by lefting and being on your knees sealing.....