do you have pellets or shreds? Normal shreds will soak in 15 mins in hot water, and are cheaper than speedibeet, but do have molasses.
I will be probably get shouted at, but even pellets will soak quite quickly ( - well an hour) in boiling water.
But why not soak over night in slightly less water than usual, then top up with boiling water about 10 minutes before feeding. Reduced water means less freezing, and the boiling water top-up very quickly removes ice and finishes off the plumping up. And they get a warm meal. If you don't have a socket handy for a kettle, a flask would hold enough to top up for one horse.