Recently being commisioned to migrate roughly 20 sites for a blue chip client under strict dealines & decomission cut off dates proved a somewhat challenging project; especially considering various dependencies within these sites required re-jigging and updating functionality (some of which had become depricated and un-supported)
Migrational work is always a headache especially when you delve into the untravelled path which its makes it easier to go offtrack at times, its also a challenge working across so many different sites / products which were developed by seperate teams / agencies during different eras,
The end result is an even greater appreciation for good application design; intelligent use of existing frameworks, unified standards and good communication and documentation, especially when legacy is the common ingredient in this recipe.
To sum it all up nicely, the potential differences in maintenance costs could vary exponentially depending on the level of understanding and quality of implementation by any team at the time that product was developed, such that the maintenance costs could easily outweight that of initial development costs.
This project once again exemplified the differences between short and long term investment within the software development rhelm, and gave contrasting perspectives of both.