I've been using DNN for 4 or 5 years now, and have developed a few of what could be termed as small web applications.  
Before using DNN I devloped system applications for companies and goverment bodies using different technologies. (not MVC I have to say!)

Whichever technology you decided to use should be based on what your trying to create, how quick you need it, what your budget is...etc..(I won't elaborate . because you understand this!!)

However I find that DNN is perfect for devloping applications quickly, it gives you a base to start with and hence saves you time.  
I think it's a myth to say the Framework restricts you, it doesn't, what restricts you is time to understand it and time to change it if you need to (it is open source, although I would try to avoid changing the core if possible).

The choice to use DNN should come down to how helpful is the CORE system to your needs, it's the core system that your devlopers will need to understand, not the modules.

I find when devloping an application in DNN using the modules will restrict you unless the module already does exactly what you need...only the less complicated.

Then their is an issue of performace, some people have complained about the perforamce of DNN, but in my experiance the only time I've had an issue was when the hardware resources where over streched.  However my experiance with DNN is only on small scale appications with limited user base where the overheads of the framework don't matter, if you need a massive user base you'll need to do some performace testing with DNN (extra work and cost).

In conclusion don't think by using DNN you going to save money....you will in the long term if your devlopment team understand it and are happy working with it, but for one application, if your needs don't match what's there already the time to learn it and then devlope your application could out weight the costs to do the devlopment in MVC.  The decision to use DNN should come down to: does the basic core help you aplication, if it does it's a big bonus, if it doesn't why use it?