Streaming webcam video. It is possible. It's very easy. And the hardware/software requirements to get started are very modest.
You could have live webcasts. And / or play back previously recorded content for students who need a more flexible schedule.
Do you need/want 2-way participation (video/voice/text)? That's internet conferencing and it's a bit more involved.
How many persons will be watching any single live broadcast? The will determine how much bandwidth is be needed to send the video stream out. And that will have an impact on the software, hardware and internet connections you can use. The largest budget item will probably be the internet connection.
What setup (hardware/software/internet connection) are you currently using for your school web site?