This would preferably be implemented as a Numeric TextBox with a Currency mask (rather than just a Masked TextBox), because a Numeric TextBox would allow for limitations on min, max and step values.

This scenario can be achieved with the RadNumericInput control by setting the "StringFormat " property as the  control will  get the culture specific symbols from the culture of the current thread. 
Available in minor release 2018.1.0315. It will also be available in the R2 2018 release.