Doing a “market survey” on bare land is not simple. With the aid of the 'Net you can search comparable pieces in your area, but might have to throw a wide net to get some idea of asking prices. If you find sold items and can determine asking price it might be possible to get an idea of the “discount” in your area. In TN (at least in our county) I can access the Property Assessors data base and determine the last selling price. This is time consuming as you are doing the research, not just reading it.
Do you have a mortgage? Is it agricultural land? With whom did you finance? Do they have an appraiser? Can you contact that appraiser directly? If so, might they give you a “back of the envelope” idea of value? My lender has a certified appraiser on staff and I’ve known him for 20 years. He has given me informal advice in the past; he also tells me where to look to verify his assessment. That’s one of the advantages of stable business relationships. 
What is the current assessed value? Does your state assess at 100% FMV? Can you easily access this data (as I can in our county)?
If you feel that the asking price is fair then if you want to “test” the price I’d “test” it lightly. If you “low ball” the seller and they get offended you won’t get very far. Do you know the seller? If not do you know anyone who could “introduce” you? The personal touch in things like this can go a long way towards a successful transaction.
Last, and far from least, do you know a Realtor who you could pay for a “informal” market value survey? They would likely do the same thing you would do personally but have better and more easily accessible “raw data.”
When land is for sale “by word of mouth” the approach you make is very important. Keep the touch light and you’ll have a decent chance of making a deal.
Best of luck in your program.
G.