The Jamison Park subdivision has taken a substantial hit already due to the economy as well as the "Reality" of the future 540. I say "Reality" because the Jamison Park folks knew 540 was coming when the neighborhood was built so this is not news to them. The price decrease can be demonstrated by looking at past home sales and current home sales. A home that is directly next to 540 vs. one inside the neighborhood will be affected differently. You really need a Real Estate Professional familiar with the neighborhood who can property work up current sales comparisons for you. This person needs to know which house you're considering. It would be impossible for someone to just throw out a "ball park" figure and it to be accurate. There are also variences within the neighborhood. For example, some homes have basements, swimming pools, and/or three car garages while others don't. Some may be close to the school and affected by the lights from football games and the park. There is a lot to consider.
If you're not currently working with a Realtor and seeking someone to represent your best interest, I'm very familiar with this neighborhood. Also, you should know 540 is currently on hold. It wouldn't hurt for you to speak to someone from the DOT to get a current update.
Best of Luck!