When you mention central A/C, do you mean split unit A/C?
Windows unit would refer to those that you literally install thru an rectangular opening in the window?
Cost for window units will very much cheaper than those split units. However, the split units will be more economical in elect consumption. As for looks, of course the split unit looks much better.

For centralized A/C, you will need to run ducting to the various outlets. This will require space below the slab & beams. You will also need space to place the AHU/ chiller unit.
Unless your condo unit have been designed for this, it would be quite impossible.
What's you reason of wanting to have centralized A/C?

Yup. That's what he was referring to. You could also check out other suppliers for comparison.