I would listen to this podcast. https://www.biggerpockets.com/renewsblog/2013/10/1... . Make sure you run the numbers for what new construction residences are going for, and subtract out construction costs, cost to install utilities, developer profit, etc, and you can get an idea of what a developer would pay for the lots. Double check the zoning to make sure you can really do what you want to do. I would find a good local real estate agent that can help make sure you get a fair price. Land has a lot of factors that can have a huge difference on the value.
Building a new house can be quite a lot of work as a back up plan. If you can buy at a discount, it will give you a lot more options. You have a lot of options for selling the vacant land with seller financing as well.
Best of luck!