Your choice to pick a home with good schools is a very common one. Many people relocate to this area based upon our school system. Perhaps it is a small bias, but I feel that more people choose Wake County schools over Johnston Co... In all my years of Real Estate, I have never helped anyone relocating here because they WANT to go to Johnston Co schools. With Wake Co, I have helped many who came to this region SPECIFICALLY for the schools.
That being said, I encourage you to research both school systems. Your criteria for a larger lot, and the price range in which you are looking will be most prevalent in Johnston County. That is not to say that you can not find the same in Wake. In fact, I have sold several this past year under $200k with sizeable yards.
I would be happy to send you listings which match your preferences, and I can even customize a search that will alert you to new listings as soon as they hit the market.
I am a resident of Southern Wake County and am very familiar with the neighorhoods and areas. Please contact me if you would like to look at a few homes.