I bought 4 of the Xiaomi Mijia light sensors (model GZCGQ01LM) last year from here: ($37 for 4, or $9.25 each)
(these are the same as linked at Banggood above, but that link didn't work for me)
All four of mine were originally on SmartThings, but last month I moved the last of them over to my C-7. I was originally using Marcus' driver
on them, but I've switched 2 of them to the newer, simpler unified driver
They are Zigbee 3.0, but people have reported that these (like the Xiaomi Aqara sensors) can be problematic and drop off. I've not had that happen with any of mine yet, but I also use Ikea smart plugs as repeaters which seems to work well with these.
Overall, these were inexpensive and so far have been very reliable.