Before locating one of the wells in my garden, I was looking at getting a 5200 gallons soft rain water cistern to put under the raised terrace at the back of the house. It was quite a cheap option, at about $1K for the tank itself (about a quarter of the price of an equivalent storage in concrete tanks). I considered buying a 13K gallon tank ($1500) to ensure maximum autonomy during droughts, as there is sufficient volume under the terrace to hold it.
The well water is actually of pretty good quality, and I was able to use it during last year's drought without issues. The only investment was a pump and a pressure group, so the rain water collection project was put on the back burner.