I am also in 1st place and have spent zero Tcash...my score is more than double the next player. My strategy is to play continually throughput the contest. I started immediately when the challenge launched, and have played almost non stop since then. I fill and send planes as soon as they land (by planning ahead), my train speed is a little over 2 hours each and I fill/send them on arrival. I send helicopter orders constantly - unless the value is just too low - and then another order loads and I send it, etc...so orders going out all the time at 1 point each, which adds up over time.
Not everyone "buys" their way in the game. I am virtually homebound so I do have more time to play than many others, which means I dedicate time to my gameplay but I do not cheat the system or purchase success..just work hard and plan ahead. Please do not assume all winners spend their way to victory, as the previous poster and I have shown that is not always true.