Don't want to pay to get into Yosemite? Frankly, you're unlikely to find a better bargain than the National Parks Pass (see some inspired orations on this topic). But if you're unmoved by these arguments and you're willing to put yourself to a certain amount of trouble, you can get into Yosemite for free. Here are your alternatives:
Not every road into Yosemite is bisected by an admission booth. The dirt road at Wawona Meadow that crosses the golf course across from the Wawona Hotel doesn't end when it disappears into the trees; it's an old stagecoach route into Yosemite, and it goes for miles and miles. You can reach this road, if you know where to look, from its outlets near Fish Camp and Mariposa. Once you get to the park, you won't find anyone waiting at the edge of Wawona Meadow to ask you for your entrance fee.
There are catches, though. It's a long drive on a rutted, unpaved road, and autos without good clearance won't make it. And there is a gate here, a few miles up the road; it's just unmanned. If it's locked when you come through, you'll have no choice but to turn around and go back, and the park, naturally enough, doesn't publish a schedule of when their backdoor gates are open. Finally, the park service checks for passes/receipts when you're leaving Yosemite, so if you're determined not to pay, you'll have to leave the park via the same long and rugged route (or leave very late at night, as mentioned below).
The Yosemite entrance booths aren't manned round the clock. If you enter the park late at night, there's usually no one around to collect your money, and you can just drive in. Of course, you're unlikely to find a place to spend the night in Yosemite if you're arriving at midnight, and sleeping in your car (overnight, anyway) is prohibited. And since the park service checks for passes/receipts when you're leaving Yosemite, you'll have to pay when you leave unless you arrange to leave at midnight, as well.
The Pacific Crest/John Muir Trail runs right through the heart of Yosemite. (Yosemite's heart is on its left side as it faces you, just like anyone else's.) Yet you won't find park attendants helicoptering in to shake you down for admission fees when you hike across the border. Maybe it's because rangers don't want to spend their days confronting people who haven't showered for a while, but backpackers get in free.
There are also several non-interstate trails that lead into the park. At the Fish Camp Snow Play area, roughly halfway between Fish Camp and the park's southern entrance, you'll find a fire road that leads to a trail that leads directly into the Mariposa Grove of Giant Sequoias. It's about a 4 mile (6.4 km) hike one way. There are also trails at Cherry Lake that lead into the Hetch Hetchy region; at Virgina Lakes that lead into the northeast corner of the park; in Bloody Canyon leading to the Mono Pass area; and elsewhere that I'm too lazy to list.
The YARTS bus service can give you a ride into Yosemite if you're west of the park in Merced, Mariposa, Catheys Valley, Midpines, or El Portal, or east of the park in Lee Vining, June Lake, or Mammoth Lakes. You'll have to buy a bus ticket, though, which may detract somewhat from the thrill of getting into the park for free.
At the Yosemite Climbing Association's annual "Yosemite Facelift" event, usually held in September or October, volunteers wander through Yosemite picking up trash (and subsequently putting it in bags). If you're willing to join them, you get into the park free on your trash-picking days. Call ahead or check with the YCA's website to make sure the getting-in-free policy is still in effect for a given year.