This is a very un-Texas thing to do but I actually used public transit not too long ago when I flew back to DFW but my car was at DAL. Budget $1.75 and about 1h15 (must change from light rail to bus at Inwood Station).

I wouldn't do it in bad weather, hot weather, at night, or with any quantity of luggage but on a mild day it wasn't bad at all.

Ironically, it was on a trip where I flew out on a business jet. I liked the juxtaposition of departing DAL on a Gulfstream and arriving on a DART bus!