Hi Suzanne, thank you for your message and for your interest in our light kit for the LEGO Disney Castle.  You can find the product options here:

https://www.brickstuff.com/store/p87/castlelights.html

The final cost depends on the options you pick.  You can purchase the exterior kit only, the interior + exterior kit, and also choose whether to add on fireworks or not.  You can see the various options on the product page above.

Don't forget to add a power supply.  We recommend the USB power cable.

Please let us know if you have any additional questions.  Thank you again!