Just recently I have very low cold water pressure but only when using multiple outlets. The cold water pressure is just fine when I turn on faucets/appliances separately, but when I use more than one anywhere in the house, the pressure is only good at the first one that was turned on. I would think if there is a clog, it would be consistent at particular locations. This does not happen with hot water, only cold. For example, if I am running the washing machine on cold, the cold water pressure in the rest of the house is cold. If I am taking a shower, the water pressure in the rest of the house is low. If I turn on the kitchen sink on cold, the water pressure in the other faucets is low. What could be causing this, and does it sound like an expensive or inexpensive fix?

Not sure about descriptions all your examples. But if this is recent event, may be caused by low water pressure entering the house. Note that all water (cold and hot) is pressurized from the single cold water line entering from outside. Perhaps the difference in which faucet/outlet inside seems lowest pressure is result of pipe-lengths along water pipes inside house, and also due to elevation (height) of faucet within house. With reduced municipal water pressure, lowest or basement floor outlets will usually have better pressure, and upper floor outlets less pressure. If low outside pipeline pressure exists, then inside pipe-run-lengths and outlet elevation heights can cause odd flow/pressure behavior. This assumes all interior pipes were originally sized and laid out correctly, and are in good condition (interior pipe diameter not restricted). If you are on municipal water supply, have them check the pressure at the street-connection; if that is good then perhaps a leak exists between street and house, which would explain the sudden/recent inside pressure problems you have. Last thought, did someone recently shut or turn down the main cold water valve inside the house, and not fully reopen that valve? Do you have any special devices on the house water system (back-flow preventer, pressure regulator, water-softener, water filter, etc.)?