Try a sandwich bag over your toes. Over your socks and under your shoes. This is one of the best things you can do. Experiment with layers. Layers can be big socks over your shoes. Or just about anything. Make sure you can move your toes and your shoes are not too tight.
Maximum heat, minimum cost, lightest weight, easy to pedal and flex your ankle = Big socks over shoes with a plastic bag over the front of you foot, and repeat.
foot
sock
bag
shoe
sock
bag
sock
bag
Covered with a neoprene booty.
below about 15f for over three hours I add a chemical toe warmer on the sock. You need to have the shoes very loose to do this. Leave the shoes loose anyway, all the layers will tighten the shoe up as you put them on.
This gives you the option of adding or removing layers on different temp days. This is important.
This is just as warm as my Sorrel thick insulated waterproof boots. Much lighter and your can pedal normally and bend your ankle. I can walk in the snow and a little water and ride with snow on my feet.
Did about 5 hours yesterday starting at 30 degrees f and ending at 18 degrees f.