While I wasn't able to talk the guy down on his $300 asking price, I did get a clean, new water tank for around $100 less than retail. I also found out he was a very nice neighbor and he offered to let me come back and fill up the tank with water in the future for free. Now I don't have to conserve water as severely as I was doing but I still want to keep my water use down to one RV tank a week. I don't like mid-week water transfer chores.
The rest of the day was spent emptying my big tank in to the new tank so that I can fix the base that it sits on. It was a very slow process and I'll have to continue it tomorrow. There isn't any rain in the forecast this week so I won't miss out on any rain collecting opportunities. I hope to re-plan my whole water collecting system so that everything is connected, housed inside the garage, and connected to the pump. I don't want to spend too much money on this thought since it is a temporary system. My main focus is still to pay off my mortgage so that I am free to build a house and drill a well without having to worry about paying a mortgage.