Yeah, ender's link is good. If you actually moved there now (or over the summer) and your son spent his senior year in the state, I expect that would easily be sufficient to establish residency. Buying a house without occupying it probably would not, given that you would still be submitting high school transcripts from out of state and everything else.
Consider involving your son in this decision. He does have some financial stake in his education, right? If he thinks no amount of money is worth moving to a different state for senior year, he'll have some loans to pay off when he graduates.