Hello, Raul,
Thank you for writing.
Instead of using
RadTextBox, I would recommend you to use
RadMaskedEditBox and use the supported currency mask. Additional information about
RadMaskedEditBox is available in the online documentation:
http://docs.telerik.com/devtools/winforms/editors/maskededitbox/numeric-masks
I hope this information helps. Should you have further questions I would be glad to help.
Regards,
Dess
Progress Telerik