When I started my production company three years ago, I had to decide which gear to purchase so I could do my job and get paid. I was on a budget, so everything had to be cost-efficient and versatile.
Here are the 5 pieces of gear that I have gotten the most use out of:
Sony FX30: My video camera of choice. Its APS-C sensor is perfect for the kind of videos I shoot, and at half the cost of its full-frame sibling (the FX3), it's much easier on my budget.
Tamron 17-70 F/2.8 Lens: This is a versatile lens with a good aperture. The zoom range of 17-70mm is big enough for me to get a variety of shots, and the F/2.8 makes the lens useful in lower-light conditions.
Audio-Technica AT897: The AT897 is perfect for interviews or talking head videos when you don't want to see the mic. It sounds as good or better than many mics that cost much more.
Zoom F3 Field Recorder: I like to record sound separately from the video and then sync the two in post-production. The Zoom F3 is a tiny stereo audio recording device that records in 32-bit float, making it very difficult to ruin your audio when things get loud.
Falcon Eyes RX-24TDX III LED Light: My main key light. It is big, breaks down into a portable size, and can change color temperature.
You can find more expensive equipment that could increase the quality of your final video, but you would be hard-pressed to find many things to maximize the quality-to-price ratio as well as these.