What steps do I need to take to get my system diagnosed without going to dealer?

What is your question?

My mpg in the past 8 months has decreased from about 42mpg (I have aftermarket chrome 17" rims) to around 35mpg now. I took my car to a "superlube" type shop to get my oil changed, the first time outside of the dealership, and they informed me and showed me that oil is leaking out of the exhaust, and swiped the exhaust pipe where there was residue. The oil consumption is about 1 quart per 4-5k miles, in the time that coincides with my decreased mpg. We went on a trip about 2k miles out from next oil change, and on the way home my oil light came on, checked the stick, and there was NO OIL in my car. My friend said maybe that could have affected the seals (?). I am not mechanically inclined, as you can tell, and I am really not fond of taking my Prius to a dealership who has obviously noticed the increased oil consumption and not addressed it with me AT ALL! Where should I go and what should I ask for?