You'd have to give more information for a true apples-to-apples comparison. As @chowzen says, a key factor is how many copies you are printing.
To offset print a book requires a certain amount of "setup" work to create the master plates. I've never paid someone to offset print a book, but I've had one-page flyers and the like printed, and the printer has charged me $25 to $100 to create the plate. I'm sure that includes some administrative overhead so a 200 page book probably isn't 200 times that, but that's the ballpark. So several thousand dollars anyway to make all the plates for a book. (If anyone on here has more precise number, please jump in. I tried Googling but the on-line printers I found all want me to fill out a form with my phone number and they'll call back with a quote. Didn't want to get into that.) If you then printed one copy and threw the plates away, it would cost you thousands of dollars for that one copy. If you printed a million copies, the cost of the plates divided by 1 million comes to a fraction of a penny per copy, practically nothing.
With print-on-demand, there is essentially zero setup cost. It's like printing a file on your computer printer: you send the file and it's done.
But offset printers are much faster than computer printers, technically simpler, and easier to maintain. So the cost per copy is small.
The end result of all this is that if you're printing a small number of copies, POD is cheaper. If you're printing a lot of copies, offset printing is cheaper. The exact breakpoint depends on a lot of factors, but it's on the order of several hundred copies.
But printing isn't the only cost. You also have to consider storing and shipping. With POD, you print copies as customers buy them. Storage cost is zero. With offset printing, you print thousands of copies. When they are all sold, you print thousands more. In the meantime you have to store them somewhere. You have to ship them to the warehouse, pay people to unload them from the truck and put them on shelves, and then when they're sold retrieve them from these shelves. And of course the warehouse costs something to build, and you have to heat it in the winter and cool it in the summer and keep the rain out and so on so the books aren't damaged. You have to keep track of how many copies are in the warehouse and where they are. Sometimes there are accidents or mistakes and copies are lost or damaged. All this costs money.
With POD, if you only sell 5 copies, you don't make much money but you don't lose anything. With offset printing, if you print 10,000 copies and only sell 5, you're out all the money you spent to print those 10,000 copies.
So in practice, the per copy cost of a POD book is usually higher than an offset printed book. But it's usually preferred by self-published authors because it requires little or no up-front investment and no risk of being stuck with unsold copies.