What's the Approximate Value of it?

Please do let me know about a rough idea as I have to decide whether to buy it or not.

Thanks

Have you looked on the banknote page? There's lots of values for all different grades there.

I couldn't find it so what does it say about the extra fine condition?

US $42 - $67

So if I buy it for $20, that's a bargain?

Yes, this one, graded XF, sold two months ago for US $44. I don't grade banknotes so I have to take your word for it being XF.