Honestly, I feel your pain. I had the exact same issues with my kit lens and it drove me crazy during a couple of shoots, especially with the focus hunting. For that budget, you really cannot beat the Sony FE 50mm f/1.8 lens. It is super cheap and way sharper than what came with your camera. It is not perfect, unfortunately. The autofocus can be a bit noisy and slow in really low light, which is something to watch out for at a wedding. But the bokeh is a massive upgrade over the kit lens and it makes portraits look legit. Just make sure you practice with it before the big day so you dont get stuck. You'll be fine tho, it is a huge step up.

Like someone mentioned, the nifty fifty is cheap, but honestly, if you are doing a wedding, relying on that older motor for critical shots might be stressful. It hunts quite a bit in low light, which is where weddings usually happen. For a bit more reliability, have you looked into the Sigma 30mm f/1.4 DC DN Contemporary? Its autofocus is way snappier and it is built much better for actual work. You lose a little reach compared to the 50mm, but you gain consistency, which matters more when you are being paid to capture someone's big day. Just remember to pack extra batteries if you're shooting an all-day event. Also, try to stay at f/2.0 or f/2.8 when you can. Shooting wide open at 1.4 is cool but the depth of field is so thin you will definitely miss focus on a moving bride.

Building on the earlier suggestion, I think you should seriously consider the Sigma 30mm f/1.4 DC DN Contemporary if you are rocking an APS-C body. It is a bit wider than a traditional portrait lens, but the light intake is just ridiculous for the price. I have used this for event work plenty of times and it rarely misses focus even when things get hectic. Here is why it works well for your situation:

• The f/1.4 aperture creates actual bokeh that you just wont get with a kit lens.
• It is super compact, so you wont look like a gear-obsessed pro at your sisters wedding.
• The build quality feels way more premium than the plastic alternatives. Honestly, since you have a wedding coming up, check out the Digital Photography Review forums or look at some sample galleries on Flickr to see how it handles skin tones. Getting the lighting right is 90 percent of the battle, so even with a decent lens, make sure you are aware of your surroundings. If you can find a used copy, you might even have enough cash left over to grab a cheap, reliable flash, which is honestly a life saver for indoor reception shots. Weddings are tough, so dont stress too much about the gear, just focus on capturing those candid moments.