Conditional price in readonly text field
Looking at your requirements I would suggest going with the data module

You could create a table with all the possible combinations. Once that is done in your content type you would be displaying the required fields such as Apartment Type, Plan Type etc. When the content is chosen you can look up in the table and get the correct pricing. 

There are some assumptions made here. The prices are fixed and known in advance and changes in price would be minimal. We only need to get the correct price defined byt the table. 

As for the down payment and EMI I presume you would have a set rules for the same which can be calculated on the go.