Cost in the end for us was ~$2k per Kw/H with me doing all the labor. Add 33% to that number for labor. So in the real work $13-14K for a 5 Kw/H for a fully installed system.
Like everything else, add to that number inflation and if you can get all the parts, since half of it comes from China. Bottom-line, it will not get any cheaper.
My neighbor has a 10 Kw/H system ($20K) and is not happy with it. Although I told him over and over again he would not be able to accomplish what he wanted to do with the money he was willing to spend, he went with what he went with. To this day, he can not understand why his system will only give him 10 KW/H a day (when the sun shines) when his house runs at 12 Kw/H a day.
The system does him little good if he has to recharge his system daily with no juice in reserves for a sunless day.
My goal was to only run 3 chest freezers, 2 refrigerators, and the electric start up for my Rinnai propane hot water heater. All told, I needed $3.7 Kw/H a day. I bought a 5 Kw/H system and I am very happy with it. Even when the sun does not shine, I have enough coming in most times, to bring the system up to 90% and still power all my appliances. After several sunless days, typically 3, then I have to plug the charger into the grid or run a generator for ~ 4 hrs.
As the items in my freezers dwindle down, I consolidate and run one less appliance.
There you go.