I found at a local manufacturer's store silicon insulation electrical wires with 2.5 and 4 mm sectional area. Not many colors, but very cheap (around 1euro/meter) and they are good quality copper, low resistance and very flexible.
Sure, model-related world uses silicone cables, but also regenerable energy requires silicone and/or neoprene insulated cables to resist in full sun heat and UV attacks.