Sorry, no experience with heated socks . . . they don't pass my crazy-gadget filter. (I love gadgets, but heated socks??? Not my cup of tea).

When stationary it is very, very hard to avoid freezing. If your toes are cold it could very well be that you need a better hat... (Your body will not allow your head to cool down, but will happily sacrifice your toes in the process...).

That being said, you can do A LOT of cheap & improvized solutions for keeping your feet warm. Something as simple as not standing on cold ground or snow makes a huge difference(a ground sheet, newspaper, whatever). You could stuff some fleece garments into a bag - any bag, including thrash bag will do. When you're at your post just put your feet (with boots and all) into the bag. As long as you're not moving it'll work. (And when you're moving you'll generate more heat and speed up the blood circulation, that'll keep you warm). You can also do a lot of improvization with duct tape and whatever material of your choice as makeshift insulation. At the other end of the scale you have dedicated solutions like overboots (most of those you can even walk with), but the good ones are so expensive you're probably better off buying warmer boots. When you do buy new boots, remember to allow ample room for an extra pair of socks.

Remember to eat and drink, preferably hot drinks.