($price > 100) is false.
false is 0, then case is executed.

You need to replace switch($price) by switch(true) so that the first case with an 
expression evaluated to true will be executed.

http://fr.php.net/manual/en/control-structures.switch.php

function myPrice($price){
switch (true) {
	case ($price > 100) :
		echo '$price = ', $price, '<br />';
		echo "Price is $100 up.";
		break;

	case (($price > 50) || ($price =50)):
	        echo '$price = ', $price, '<br />';
		echo "Price is $50 and up.";
		break;

	case ($price >25):
		echo "Price is $25 up.";
		break;

	default:
		echo "Price is no more then $25.";
		break;

	}
}

When parameter $price is less than 50, for example 30, execute myPrice(30), 
actual result always is:

$price = 50
Price is $50 and up.

Because you have $price=50 there instead of $price==50