Count your blessings, then - fortex bowls are $9-$12 here.
I have picked up a few at garage sales but the rabbits chew them to bits fairly quickly; I doubt it's very good for them, and they're meat rabbits and I'm not wild about eating fortex either. They also tend to throw them around, dumping any liquid water and making any ice in them unavailable since the bowls invariably end up upside down.
The rabbits are in a barn so there's not much issue with wind chill, but we generally see temps in the low teens and less, with stretches of below zero. Water bottles freeze quickly here too, especially the metal tubes which will freeze solid before the water in the bottles. Also, the bottles often crack in the process of freezing, especially if they are completely filled, so I put them away in the fall.
I use both the cheap plastic bowls described above ($1 ea), and ceramic crocks I find at thrift stores. The two keys to keeping crocks from cracking is to use crocks that have a taper on the inside, so that they're slightly wider at the top than the bottom, and to minimize big temperature changes. We give our rabbits hot water, but I don't pour hot water into cold crocks. I either bring the crocks inside to thaw and replace them with warm ones, or we sink the frozen bowls into a bucket of warm water for them to release the ice and warm up, to be re-filled with warm water. We don't have to "crack the ice out" which is not much fun anyway. (We do sometimes twist the plastic ones when it's warm enough that the ice will let go.)
Honestly, though, there doesn't seem to be a perfect way to provide water in deep winter, so we just rotate our practices when we get tired of the problems with one.
The biggest "trick" we use, though, which really seems to help the rabbits stay in good condition, is that in addition to giving them water twice a day, we give a each of them a treat-filled ice block. We freeze water in old yogurt/cottage cheese tubs, adding something tempting like apple cores or carrot peelings to be frozen into the middle. We leave these blocks in the cages all the time, and the rabbbits love to play with them and chew on them - they get hydrated, entertained, and good tooth-trimming round-the-clock.