First you will need a SDXC card which has much larger boundaries than the SDHC card - 64 to 128 Gb.
Then you will need a camcorder with an external mic socket (or an independent recorder)
Finally you will need a decent mic, possibly a super cardioid electret condenser.
My setup (as an example) is a Panasonic HC-V800 HD camera and various electret condenser mics, in particular a super cardioid mic for recording at a distance.
But for your example I would use my Tascam DR-60D MkII linear PCM recorder with two Berhinger C-2 condenser mics located close to the choir. The DR-60D has a feed directly into the camcorder to sync the audio track
Then I would use my video editor (Corel VideoStudio) to sync the audio with the video, render the file and burn a DVD directly.
Camcorder in-built mics are OK provided the camera is close to the choir and the room is "sound dead" i.e. no reverb or external noises. For a clean recording you need to consider how you can record the sound without outside interference. (possibly more important than the video) Many people do use an independent audio recorder and then sync the video with the audio later.
Panasonic camcorders have an additional benefit, they are recharged and can be run from a 5V USB source. (any 5V USB source, mains, car, battery) For long recordings I use a "Power Bank" sold to recharge mobile phones etc. My 20,000mAh AUKEY power bank will run the HC-V800 and the DR-60D together for 6-7 hours.
We are looking for a camera for a local singing group. Our budget is $500 or less. We need the ability to record up to 1.5 hours continuously (not segmented). It needs to have good audio recording quality. It needs to record in a format that easily converts to a DVD. What do you recommend? Thanks in advance.