The KG1 C is 5'1" and is a nice little grand. It won't really fill a concert hall, but a small church may get away with it. Also, 3900. seems to be a fair asking price, however, it is a 35 year old Asian built piano which means it may have a good amount of wear and tear such as corroded strings, weakening pinblock, worn hammers and sloppy flange bushings. Make sure an experienced player takes their time and plays it a lot. I'm not talking etudes. Every key, scales are good, bottom to top and have an unbiased technician check it for you for a fee.
If it has been thoroughly regulated and had the hammers shaped, sounds good, feels good, everyone likes it, could be a good buy.