Client sees appointment times in his own local time

I sell appointments to people all over the world - therefore they all have different time zones; my time zone is +2 GMT.

I need clients to be able to book appointments in their own local time and for me to be informed on the appoint in MY local time

Example. A client in California who is 9 hours behind my local time zone will book an appointment for 7am local California time. The system will ensure that I am informed that I have an appointment starting at 4pm in my own local time.

(the product Schedule Once does this for $5 per month but I prefer to pay once for a WP plugin)