How cold does it get where you are?
The main things for keeping feet warm in winter are two things:
keeping out wind and water
I wear winter boots one size too big, so I can get an extra pair of socks in without making them too tight. If they are both thick, knitted wool socks, I can cycle in temperatures down to -10 C. (whether I want to is another thing
For insulation layers, you can add them outside or in, but you need to add them. If you are cold wearing your current boots, and cannot buy boots sized big enough for another pair of socks, you almost have to add something on the outside. For blocking wind & water, you can use home made solutions, like plastic bags between your socks & shoes, home made toe covers, or rigging a wind/splash shield for your pedals out of plastic containers or milk jugs.
The extent to which you need to do these things depends on how cold it gets where you are, and how much your feet feel the cold. How you deal with it depends on your time versus money values. I'm sure that you can figure out something that works for not too much money, but it will likely take some trial and error with home made solutions.
“In some ways, it is easier to be a dissident, for then one is without responsibility.”
― Nelson Mandela, Long Walk to Freedom