If I'm correct 75062 is Irving. So is the location of the lot appreciating or depreciating? That is what you ask
yourself and is it worth it to you.
As Lynn states, without more specific details there are only vague answers. If your buyers agent is experienced in this type of real estate you are in good hands, if not I will gladly be of service. Best of luck, Sam!
Once the value of farm land converted to residential lots has been established, the appraisal may not change over time and thus become lower than its true value. However, appraisers have been under a lot of pressure to give extremely conservative values, because they do not want a regulator coming back to them and claiming they committed an error, intentional or unintentional.
Ask your Realtor for some guidance on whether the price asked for the lot is reasonable or not. You can also check values in an area with a simple on-line tool such as http://www.DallasHomeValueReport.info