What You'll Need
I made my mozzarella from a kit. You may have seen these kits online or at more DIY-leaning kitchenware stores. Roaring Brook Dairy sells one ($18.50), and there's also Ricki's Cheesemaking Kit ($24.95).
I've used both over the years, and they're more or less the same. Both come with instructions, a thermometer, citric acid, cheese salt, and rennet.* The difference? Ricki's comes with cheesecloth but no gloves while Roaring Brook comes with latex gloves but no cheesecloth.
Really, though, if you already have an instant-read thermometer and are comfortable following a recipe off the web (here's one), you can gather the essentials for far less. Look for citric acid at health-food stores. You might be able to find rennet, again, at a more DIY-leaning kitchenware store (Brooklyn Kitchen in NYC, for instance) — or order rennet online from cheesemaking.com, where it starts at $6.50.
You'll also need a gallon of whole milk. As high-quality as you can get. The fresher, the better. And this is crucial: IT CANNOT BE ULTRA-PASTEURIZED.
I've made mozzarella with regular ol' grocery store whole milk and with fancy-pants family-farm, gently pasteurized, non-homogenized full-fat milk. Guess which one makes better cheese. The less processed one, yes.
I'm not going to make this a step-by-step guide, because there are plenty of those on the web. If you did not catch my link above, here's a recipe you can follow for making mozzarella. Peep the slideshow here for a sort of general visual overview of what you'll have to do.
Is It Worth It?
OK, so remember how I mentioned opportunity cost and economies of scale? While I slowly pressed the whey from the curd and dipped my hands in the painfully hot salted whey to stretch the cheese, I had plenty of time to contemplate this stuff.
The opportunity cost, of course, is the amount of money I choose to forgo in order to make this cheese. Say my time is worth X dollars. I could theoretically be making X dollars instead of making cheese. If X is greater than the cost of the cheese, it makes no economic sense for me to separate the curd from the whey.
(This all reminds me of an article on Slate by Jennifer Reese, in which she explored whether it's worth it to make certain pantry staples or whether you should just buy them.)
Personally, I did not find making this cheese worth it — especially given my lackluster result. Yes, there is an educational component to the endeavor. And I do think that it's worth it to make mozzarella once or twice to learn how it's done. Then go back to buying it from a good local fresh-mozzarella-maker. Which brings me to ... economies of scale. Your local mozzarella-maker benefits from this other basic economics concept. With all the equipment and know-how and time, it's easier for them to make large batches of curd -- thus cost and effort decreases per pound of cheese.
And believe me, after a couple hours of messing around for a less-than-softball size hunk of cheese ...
* Ricki's is vegetable-based rennet; Roaring Brook's makes no mention of the rennet source, so folks looking to avoid animal-based rennet might give RB a shout to find out which it uses.