If it is desirable gear and you take really good care of it, it will resell for as much as 50%-75% of best new gear price you can find. That said, a thru hike is a lot of miles to keep gear in excellent condition. Know yourself and it will help you in this planning process. Another option is to buy it used, rather than new. I've occasionally bought gear used, taken good care of it over a few years of use, and sold it for the same or more than I paid for it. I take really good care of my gear. Not everyone does.