Some cheap alternatives for wires-
RCA's- the cheap kind with the thin black cords works fine, I have never heard an audible difference between them and the 69$ name brands.
Speaker Cable- Lamp cord is a decent 16 gage equivilent, although speaker wire is generally not that pricey so you don't really need to skimp.
Power Cable- Jumper/welder cables will work just as well at a fraction of the cost of the name brand stuff, and you can find some really nice flexible welding cable if you look around.
The concerns about corrosion are a little exaggerated, a cars factory wiring is made up of regular wire and you see alot of 20+ year old cars driving around with the original battery cables under the hood, you just need to do a little maintenance by cleaning the battery terminals every few months with baking soda and water. I would not reccomend using crappy speaker cables in your doors though, because you don't want to have to take apart the door and replace those in a few years, but cheap RCA's and power cable will work like a charm.