I think Cost should not be the factor for choosing the tool, if you are going for a proprietary automation solution, you should see which tool support your application better and simple to use download both of them and give a try..
If you cost is the major factor, go for some free/opensource tools.
AutomatedQA Test Complete is generally cheaper than QTP and has support for .NET apps like you're describing. I used it for the same type of application. This was a couple of years ago, but I found it much less user-friendly than QTP, though it did have advantages as well, like being able to choose from a few different scripting languages.