Assuming that you only rewire your amp for sub only, then you need 5.3M of power wire, with 0.3M is for ground and 5m remote wire. Like that also he want to charge you 100+? If yes better you let me do it. I will charge half of his price, is actually very simple to wire up the amp from front to back, only you have alot of work to do, like take out the seat, disconnect the battery terminal, take out the carpet and so on. If we diy, it maybe will take you half day to do it.
You can ask him how much is the workmanship only if you bring your wire along? what is your new amp RMS rating? I have power wire for sale that can support up 300-400watt RMS. I bought 20M and 1M cost me rm4.5, so now I got extra and if you want I can sell to you.