You have to be very careful about introducing and detecting respondent biases - existing ones as well as ones you induce with the material presented.

This is beautifully demonstrated in the on going shouting match over Reproductive Rights. Each side tout studies after studies showing concrete proof that the majority of the population supports their side of the arguement.

The trouble is the flawed tools used. Example: Answer each question Yes or No

Do you believe that a woman should be forced by the state to have a child?

(A great majority will howl NO)

Do you believe that babies should be killed?

(Again, you will find very few NO votes)

The phrasing and timing of questions is tremendously important.

There maybe some research studies already done that can give you numbers you can use for stuff like political bias but for your case you might try to isolate some other non-volital area to show a tendancy of people to be biased from media exposure.

Basically this would be focusing on Advertizing and how it impacts perceptions. You could takes something as harmless as a large scarf, have it on hand for the respondent to touch, ask a question about buying intent (to get a baseline), then show them some form of media (pic, video - again what resources do you have) one showing the scarf AROUND THE WAIST of a beautiful young woman - then reask purchase intent (10 point scale). This is one Test Group, the other Test Group would be shown the same scarf used in another accepted but less attractive manner (used as a head scarf with a not so attractive person, used as a traditional, ethnic head garment, some other manner) and ask those people purchase intent.

What is the difference between the groups? Now at this point you might need some statistical software like SPSS or help cranking out the formulas for significance testing to see if their is a trackable shift (you need demographics also - male/female/age/income/ethnic background/etc. to see if one cell or another is more driven with your two stimuli.

Someone else may have a simplier suggestion, look up Marketing Research and do some reading there. Is there a local college with a Business department, call them up and so on.

Media Bias, you could work the arguement that advertizing shapes perceptions. There are a number of studies already out there to model or guide you. Ads are used in everything from Politics to Religion. One way to get the competition's notice is to find something unique, or not obvious, that You Know - what drives decisions (buying patterns): Name recognition, concept association, price, whatelse?

I would think trying to prove Media Bias as in the myth of the Liberal News Media influencing an election, would take a lot of money and time. You need to steer away from areas that people are already firmly entrenched on. Because people were already heavily biased, and even with the propaganda highly biased, I don't think too many hard core Republicans were even slightly influenced by Michael Moore's 911 Mocumentary.

Good luck