It is best to ask a real person, not try to do it on your own, because evaluating comparables is a skill that takes training. Otherwise, you might wind up comparing apples to oranges, truly.
If you want to see prices for sale and recent solds, check out this handy little spamfree website www.DallasHomeValueReport.info
After you have seen the data, ask a Realtor for an opinion about the house you're interested in. If your Realtor isn't helping you do this, get another Realtor.