Hello George. You are right in saying that underground rainwater harvesting systems can be costly. This all comes down to what you would like to use the saved water for. If you would like to water plants and relatied gardening activities then a simply water butt on the side of the house would be a very cost effective solution. Other systems such as greywater for toilets are effective but again can be quite costly. If you would like me to have one of our experts contact you to discuss any potential system please send me your details to enquries@eviee.co.uk. Thanks.