You can buy white lithium grease from hardware stores for not a whole lot. Yes, there are airsoft-branded greases and oils, but honestly the white lithium you find in home hardware is the same as the white lithium at some airsoft specialty store. You're paying for the brand name, and the cute packaging it comes in. The pill-bottle like container at home hardware is the same, just make sure you do get white lithium and not something else on accident.
Do NOT skimp on the silicone oil, though. Must be 100% silicone oil. Most people usually just end up ordering a bottle or two to keep for maintenance, and that's if they even need it. Silicone oil is usually used for mags that have feed problems and need it oiled up for smoother movements. You can also use silicone oil on your hop-up sleeve to get it to fit in your hop-up unit if it's too tough without it.
Primary: Custom WE M16A3
Secondary: KWA MP9
Side: Custom WE M1911A1