For the availability and cost of spare parts, we would suggest you walk into the nearest service centre as they will be the better person to assist you. You can click on the following link to see the details of the nearest service centre and selecting your city accordingly - Service centre.
Both Ativa i and Dio are the most demanding scooter. Honda Activa i churns out good mileage and power as compared with Honda Dio. So, in terms of mileage, performance, and stability Honda Activa i will be a good option in comparison to Honda Dio. Moreover, we\'d suggest taking the test ride of the options so that you can understand the difference and finalize your decision - Bike Showrooms