For those using taxis these are the going rates:

(from http://www.dallastaxi.com/rates.html)
FARE SCHEDULE
$2.25- Initial Meter Drop
.20- For each 1/9 mile
.45- Per 1-1/2 Minute Traffic Delay/ Waiting Time
2.00- For each extra passenger (Up to rating seat capacity)
8.00- Minimum for trips originating at Love Field Airport
1.00- Love Field loading fee
18.00- Flat rate for each trip either originating at Love Field Airport and terminating within the Dallas Central Business District or originating within the Dallas Central Business District and terminating at Love field Airport
40.00- Flat rate for each trip either originating at the Dallas Fort Worth International Airport and terminating within the Dallas Central Business District or originating within the Dallas Central Business District and terminating at the Dallas/Fort Worth International Airport
15.00- Minimum for trips Originating at Love Field Airport and terminating within the Dallas Market Center Area or originating within the Dallas Market Center Area and terminating at Love Field Airport
32.00- Flat rate for each trip either originating at the Dallas/Fort Worth International Airport and terminating within the Dallas Market Central Area or originating within the Dallas Market Center Area and terminating at the Dallas/Fort Worth International Airport

Look at this page for a list of Taxi companies in the area: http://www.visitdallas.com/visitors/visitor_resources/category.list.php?category=1713&location=&search=&x=6&y=6