Sort numbers by numerical value
===

I added a code that allows me to sort WordPress posts by custom fields. I'm trying to sort the posts by prices, but it's sorting by the first number and not the value:

    $116.99
    $12.95
    $149.00
    $15.99

Instead of: 

    $12.95
    $15.99
    $116.99
    $149.00

How can I get it to sort properly?

Here's the code: http://pastebin.com/Pe5yfvrE 

I took it from this discussion, but it was left unresolved there.. 

http://wordpress.org/support/topic/sort-posts-by-custom-field-in-backend