Price for land to develop multifamily near downtown Nashville

[Mark Matos]

The seller approached me to sell 5 acres of land less then 5 miles from downtown Nashville. The land is zoned for the building of 21 units (the project was approved by the city). He inherited the land

along with many other properties from his father, who was a builder and passed away. He is selling it all. 

I have no experience developing anything but I have a hunch that this might be a great opportunity. My question is: What would be a good price to pay for the land?