BJ, as far as I know:
- 75 K should buy you a brand new corolla (at least the basic version). A 2009 Lexus (basic sedan) will cost probably twice that. You can check the car classified in this site and qatarsale.com

Of course you should factor the loan payment to your car. A 48 month payment of 75K will set you off almost 2 K a month (inc. services and operational cost). Also factor in some ready fund to pay traffic fines....

- Coffee shop and dining out will cost you say 200 riyals per person per visit. How much extra for Alcohol and/or 'companionship' ;-) you'll have to ask others..... hey, I'm here with my family....

- Yes air tickets will be taken care by the family. But I'd suppose that you will have to pay your own for sundries etc.

Hope it helps
Cheers
SK

- Medium level shopping, may be 1000-2000 (depend on what you call medium level).