The keys to running an efficient public transport system are to figure out where the people most likely to use it live, and to determine where they need to go. For now, I'd run three North-South two-way routes along Collins, Cooper, and Fielder, from Green Oaks to I-20. This would serve most of the people in Arlington who don't have cars (college students, ghetto dwellers, and "immigrants") and allow them to get to the retail and service jobs they work at (Parks Mall, fast food strips, etc.) I'd also run three East-West routes crisscrossing these: One along Randol Mill Road from Eastchase to 360; one down Division from Dottie Lynn Parkway to 360; and one down Pioneer Parkway from the Fort Worth border to 360. (The Randol Mill and Pioneer routes would link to the Fort Worth T at Eastchase shopping center and the Arlington Police Academy respectively.) I'd then run a two-way perimeter route around town on Green Oaks and up the 360 service roads. This crisscross.perimeter system would enable most riders to get to within walking distance of home, work, and shopping, and would serve the college campus, the stadiums, Six Flags, the airport, the lake, and the downtown area well. I'd also run nonstop express buses from the Parks Mall and downtown to the Hurst/Bell and CenrePort/DFW TRE stations. Add to this the TRE line that will eventually be established on the UP right-of-way and Arlington will finally ben connected to the DFW area at large rather than remaining an island where the natives have to own a car to survive. As for the cost: Arlington hasn't hit the state sales tax cap. A 1/8-cent sales tax would raise more than $5 million per year. The City could simply post a bid notice and contract with a private operator to run the system for $5 million bucks per year. There must be a dozen companies in Arlington alone that could organize and run a public transit system I've described for five million bucks; hell, I could probably do it myself. If no company could run the system for $5M, the system could be pared back to a size that could be operated for under $5M per annum.
(Fun Fact: The City of Arlington is kicking in $325 million in funding for the JerryDome. This money comes from a .5% increase of the city's sales tax, a 2% hotel tax, and a 5% car rental tax. And all this for a stadium that few Arlingtonians will ever be rich enough to enter.)
We will have public transit in Arlington, sooner or later. Traffic, the Jerrydome, and the inevitable rise of gas prices will eventually end the practice of everyday travel by private car in Arlington for all but the rich. When gas is only available at $20 per gallon — or is "for government and emergency use only" — Arlington will have public transit, or it will cease to function.