Economics 101 in two minutes (someone please time me):
The price of an item is determined by supply and demand.
We can plot supply as a function of price. The x axis is the price and the y axis is the amount that could be produced for the price. The amount produced is zero for price zero and increases as price increases.
We can lay the demand curve on top of the supply curve. The demand curve is how much people would buy at a given price. It is infinite (or at least very high) at price zero. As the price increases the amount that could be sold at that price decreases.
At some point, the curves intersect. Under free market conditions, the intersection is the price at which the item is sold.
What the others here have talked about is why the supply curve for pork is lower than for beef. It may also be that the demand curve for pork is also lower than for beef, meaning that for the same price, people prefer beef to pork. Which would you prefer?