I am a little confused by your question about George Mason since you said you don't want to drive to work. George Mason University is probably 10 miles from Reston so that isn't an option if you don't want to drive. However, while that area is nice (and adjacent to the City of Fairfax) housing will be less expensive as compared to Reston.
Towns to the east of Reston will be more expensive than towns to the west of Reston. If you are asking about the eastern section of Reston as opposed to the western section of Reston then I don't think there is a big difference and pricing will be more a function of how nice the community is, the amenities and, of course, proximity to Reston Town Center. Condos near the Town Center are selling from low $300,000s to $500,000.
In general, I think you may have a challenge on your hands to get inexpensive housing in easy walking distance to the office centers in Reston. Reston is a relatively new "town" developed over the last 30 years. Aside from the office buildings in the town center much of Reston is kind of spread out with pockets of office complexes, making it difficult, although not impossible, to walk to work. Biking to work would be much more feasible, except during very occasional winter snowstorms. If you want to share where the building is located that you will be working at I may be able to give you better ideas.