This often forces you to set up the furnace thermostat driving up your utility bills. Since your budget is limited, you will not be able to have the walls professionally insulated. If you have full masonry walls, there is no gap inside the walls for insulation anyway. Adding insulation on the exterior is a major job. Adding insulation on the interior surface loses floor space.
Every house can use some additional shelves, cabinets or an extra kitchen pantry.
Building a closet or storage area with a tight-sealing door creates an insulating dead air space. For even more insulation, attach a layer of insulation to the back of your new storage area. Rigid foam insulation provides the highest insulation value and is easy to install. Check your local fire codes because they may require foam insulation to be covered with drywall. If you are not handy with tools, build simple wooden shelves.