How I can Use Regex Method To Validate Float Value ?

How I can Use Regex Method To Validate Float Value ?

i use WPF & c# 2010
i have textbox to enter Price .
i use DataErrorValidationRule.
i want to Force the user to enter Float value.
How I can Use Regex Method To Validate Float Value ?
is there Better Way To Validate float Value ?
thank you ....