I assume you mean a private (not shared) ride, even if it is through one of the shuttle companies? Some do offer private service, e.g. you can check Super Shuttle's service online. I can also give you the number of the guy I've used for the past couple of years. You can specify private service, though that is what he usually does anyway. (Disclaimer: he is a neighbor so there is a personal connection.) Taxis are readily available in the taxi lane outside (they may have to wait a few minutes if they come in at an odd time) and will cost about $50-70 to go downtown. What is your budget for transport?