My family and I don't own any genuine cold weather gear. Just a cheap Walmart tent, some 1.5" self inflating mattresses, some run of the mill Coleman bags, and a half a dozen blankets, layered on top or on bottom as necessary for padding or insulation. We've learned to make what we have adapt rather than spending a lot of money on different gear for different conditions.
When it comes to keeping warm, the most effective thing for me and my family has been to pack as many people as possible into as small a tent as possible. We stuff the 4 of us (myself, the wife, 6 yr old, 3 yr old) into a 2-man tent. We own a 4-man tent and 2 2-man tents that all zip together into a large compound if necessary. But over the years, we have slowly migrated to the smallest package possible and now sleep all of us in a single 2-man. Just enough room for bodies (we leave all non-sleeping gear in the vehicle).
If you have kids, take them camping with you. A 2 year old puts out the BTUs better than any tent heater on low could. It's amazing how hot kids sleep. With your first kid you'll think they have a fever every night, but that's just how they are.
When camping in sub-freezing temperatures, we put a $0.99 reflective emergency blanket on top of the tent, but underneath the rain fly. This reflects quite a bit of heat back into the tent.
I sleep nude or just skivvies to let the bag hold the heat in...
...The nude sleeping thing is a common misconception. It works because people go to bed with tight fitting clothes or clothes that are damp(it you have been wearing them they are damp). As long as the clothes aren't constricting or damp or too bulky to allow you to now compress the bags loft they won't hurt the temp rating. Dead air space is dead are space.
Like mesha said, if you've been wearing your clothes all day, there is ALWAYS some amount of moisture in them, especially undies and socks. I always put on clean undies and dry pajamas before I go to bed. Same thing in the morning, put on dry clothes (undies included) before you climb out of the tent and you'll adapt to the morning chill a lot quicker.