In this post Extract only numbers from a String,
I described a method of extrating numbers from a string using split and concatenate technique

In this post Regular expression,
I described a method to extract whole numbers if a specific digit is found

Consider that you have a situation where you need to extract only amounts from a text

Here is a way to do it Consider this example

declare @sample table
(
        data varchar(200) 
)

insert @sample

select 'The amount is $87623.63' union all 
select '$87.21 is paid' union all 
select 'you have credit of 1000 US Dollors thanks' 

 select 
        data,
		substring
		(
			data,
			patindex('%[0-9]%',data),
			datalength(data)-
			patindex('%[0-9]%', reverse(data))-
			patindex('%[0-9]%',data)+2
		) as amount
    from 
		@sample

    where 
        data like '%[0-9]%'

The Output is

data                                              amount
----------------------------------             ---------------
The amount is $87623.63                           87623.63
$87.21 is paid                                    87.21
you have credit of 1000 US Dollors thanks         1000