Costs for a typical solar water heating system is around £4,800 (inc VAT at 5%).
Savings are moderate - a solar water heating system can reduce your water heating bill by between £50 and £85 per year. It will also save up to 570kg of CO2 emissions, depending on what fuel you will be replacing.
Maintenance costs are very low. Most solar water heating systems come with a 5-10 year warranty and require little maintenance. You should take a look at your panels every year and have them checked more thoroughly by an accredited installer every 3-5 years, or as specified by your installer.