Use Priceline
Priceline.com works wonders for cheap hotels in Dallas and Ft. Worth. However, you have to do your research. Find out which districts offer 4 star hotels in the districts you like. Then lowball your offer (4 star hotels usually go for ~$60-70) and if it is rejected, up your price about $5-10 and increase your search area with another also containing a four star hotel. I did this in Ft. Worth last month and got the Renaissance Worthington for $52/night on a weekend, and they classified that hotel as only a three star.
Good luck. If it works out, I'm curious as to what deal you got.