Is this calculator ok?
http://coinmill.com/BTC_USD.html (is it up to date?) If you know better please post.
I want to buy btc for 50$ what is best site to buy btc for low money?
Am asking for calculator because i dont want overpay btc and then wait 6 months until i see 0.1$ profit

Go to a Bitcoin club and wait until they are drunken then you will get it cheap.