At $8.99 for 100x2.5mg, Serious Nutrition's Yohimbine seems the most cost effective.
Yohimbine is a supplement that has been linked to fat loss when taken in a fasted state. It has certain side effects that you should be aware of. It raises your heart rate (increase dosages to recommended slowly, don't dive in), and so do NOT do high intensity exercise like weight lifting until it works out of your system. Because of this it is not appropriate for people with hypertension, high blood pressure, or anxiety issues. Only do low intensity exercise while feeling its effects - trust me.
Yohimbine won't accelerate fat loss, that isn't the point, rather it helps to ensure that fat is lost from all places, and not just the arms and face. Be aware though that it will also mask fat loss with water retention, so keep that in mind. If you are heading into a competition stop taking it a couple of days prior to the big day!