My money is on 1993.
You can date the components: http://www.vintage-trek.com/component_dates.htm . That should give you a pretty accurate idea of the frame age if the components are original.
Nice find! Bikepedia might Help. Goes back to 1993 for the Hardrock. Doesn't list colors or seem to have pictures for that far back, but it does list stock components. Assuming there are some stock components left, the Bikepedia info might help you pinpoint the year.
Wow what a bargin! I just bought a white one from the 90's and paid $125. It has new tires, tubes, chain, and was just tuned up but still the price difference is almost $100. Great deal!
Nice find! Like the others,I would say a mid 90's bike. Looks to be in good shape.
Great deal, hope u enjoy it :)