These are few simple steps which can save costs for you in a major way. If you have a third party development vendor, it is sure that they would avoid all of these to keep their billing on the higher sid, unless you enforce and review these basic steps all the time.
Standardize: Every organization must standardize the platforms, coding language, database and messaging layer across the organization. This will help exploit the resources to the maximum and avoid rework.
Reuse: You must maintain quality approved standard code libraries along with the description which should be stored in subversion or any other easily accessible place. This should then be exposed to all developers and architects who can make use of standard components without bothering to rewrite. This step alone can save upto 50% of development cost in a matured environment.
Exploit Open Source: Resources available through open source should be exploited to maximum to avoid redoing development which can be simply cut and paste. However, this should again be regulated through processes and standards so that developers do not waste time downloading same codes several times.
Integrate: Using standard plug-in with your available systems through messaging platform, it would be very easily possible to integrate your applications and unleash the power of your application. In a matured development environment, using pre developed plug-in and database access can be exploited to deliver business needs rapidly.
Revise and upgrade: Change is the way of life. Even if not required for the moment, it is always prudent for development teams to keep their codes ready to take on new technology and platforms to avoid larger development and upgrade costs at a later date. An application available on Client server should be upgraded to web and from web to mobile device and so on.
Such simple but disciplined steps would go a long way in giving business what they want rapidly and something which no vendor can ever replicate. This will also eliminate the dependency on individuals which is the biggest pain point in IT industry today.