What are good used sport/mid size luxury cars That I can buy for less than $10k?

Consider a low mileage Mercury Grand Marquis, Lincoln Town Car, or Crown Victoria.  They get 25+ MPG on the highway on regular gasoline.  They can be bought with low mileage for less than $5K and are reliable and durable.  Ford built jillions of them so finding parts and someone who knows how to work on it is easy.  Yes, it's a bit old fashioned but a V8, rear wheel drive car with a full frame is a great way to build a car.  I miss mine.  The fellow who has it today has passed 300K miles and its doing pretty good.      

Toyota Avalon. Great car. A "sleeper" on the market. 

Lexus, Acura, Audi, and Mercedes are examples.  But considering your financial situation, you definitely do not need a midsize luxury car.  Given your budget, you can afford a $700 Trek bicycle.  Here is a picture of my son on his bike.  That was in January when he was interning at Google.