A professional installer will strive to provide an accurate costing which clearly shows items that are included and the odd item that is not (electrical work perhaps).
As a guide, a small garden with drip or low volume irrigation for the borders and planted areas is likely to be in the region of £1,500 - £2,500. This is likely to be supplied via the mains water supply and would include necessary components to conform to water regulations and to provide automatic control and a rain sensor.
A medium sized garden with pop up sprinklers for the turf and drip / low volume for the borders, water storage tank and booster pump, automatic control and rain shut off device is likely to be in the region of £4,500 - £6,500.
Understandably there are a number of points that can have an impact on installation costs such as ease of trenching, obstructions (driveways, trees, hard landscaping, services etc), proximity of mains water / power and level of reinstatement.
You get what you pay for
When choosing your contractor, you should be wary of those who offer to charge you significantly less than other contractors. There are many cost cutting techniques that inevitably compromise the performance, efficiency and life expectancy of your system.
Above all, you should choose a company that you can trust and with whom you feel comfortable. It is important to install professional products such as those supplied by LWS.
The Rain Bird product range is used by professional installers across more than 120 countries, and choosing a contractor who uses Rain Bird products is the best way to ensure the job will be done right.