I recommend working with a Realtor in Montgomery County who specializes in land & ranch sales. The seller usually pays the buyer agent's commission so there is no reason not to use a professional in this case. A Realtor will help you in negotiatations and can tell you what the going rate for acreage is (so that you don't pay more for land than it's worth). They may also be able to negotiate a lower price since you'll be paying cash. The seller will most likely have a Realtor protecting their interests, and so should you.
Best of luck!