As recently as the first quarter of this year, there were only a handful of 360 cameras. Now the market is flooded with 360 cameras. Here are several low-cost 360 cameras. Please note: I haven't tried any of these. I did buy a cheap 360 camera once, and it was horrible. I would take the claimed specifications with a grain of salt. I would also be cautious of reviews because some of them could be fake.
1. Geektopia and variants (around $100 to $160). This hemispherical 360 camera has a dedicated waterproof case with a GoPro-style mount and a variety of attachments such as a helmet mount and a bike mount. The photo resolution is claimed to be 12MP (3472 x 3472) and the video resolution is 1920 x 1080 @ 30 fps. However, because the sensor is only 8mp, the 12mp photo resolution is likely to be interpolated (i.e., with no additional detail). The waterproof case is supposedly rated at 100 feet. The cheapest version seems to be this one.
2. Detu and Joyplus (around $140 to $150). This hemispherical camera captures 8mp photos and 1080p videos.
3. Amkov and variants (around $120 to $160). AMK100S is a hemispherical 360-degree camera marketed as a sports camera and comes with a waterproof enclosure that supposedly works up to 30m. The video resolution is 1920 x 1440 @30fps and the photo resolution is 3264*2448. Here is a cheaper version.
4. Cube 360H ($113) is a hemispherical 360 camera with a GoPro style attachment. It has a Sony IMX078 12MP CMOS sensor. It is called '4k' but I honestly don't expect it to be actually 4k. It is waterproof to 10 meters (without the need for a case) and has a dedicated remote shutter.
5. HDKing Panoview and variants (approximately $99 to 120). This is an egg-shaped hemispherical 360 camera. According to the listing, video resolution is 1920 x 1440P 30fps and photo resolution is 3264 x 2448. There are several versions of this camera being sold on Amazon, such as this and this. The cheapest one seems to be this one.
6. Turnmeon ($85). A hemispherical 360 camera with a waterproof housing. Video resolution is claimed to be 1920 x 1080 30fps.
8. Elecam 360 and variants (around $160). This is a fully spherical 360 camera with two lenses and two OV4689 sensors. The photo resolution is 3008 x 1504. The video resolution is 1920 x 1080P @ 30fps. There are other versions of this camera such as this one.
I don't know about the quality of the cameras listed here, but I can assure you if you're just curious about 360, a poor quality 360 camera will give you the wrong idea about 360 photos and videos. if you're looking for a low-cost 360 camera, there are two that I know are pretty good: the Insta360 Nano ($220) and the LG 360 Cam ($200). I will be posting a comparison between them (and compared to the Theta S and Samsung Gear 360).