Texas is called a "non-disclosure" state, which means the prices that are paid for real estate are protected and can be hidden from public view.
You can guess what price someone paid for a property by looking at its listing price. A Realtor in the area where you're interested normally has access to sold prices in MLS, but these cannot be published, such as on a website. Realtor MLS rules require that the person who receives the information be known by the Realtor before any disclosure of private MLS data can be made. Data from other public sources can be used.
Trula members should not be disclosing sold prices from MLS in Trulia without permission of the principals.
There are other sites that estimate the value of properties, such as Zillow, but frankly we don't know where they get their information from.
Your best bet is to ask a Realtor about a particular property.