I think the 7500FX was the predecessor to 7.5FX (and others in the current FX line.) I've seen them on Craigslist before. At some point Trek made the FX the "flat bar" hybrid and the 7000 series their 700c tire comfort bike line with higher bars and a suspension fork.

Tune-ups run $50-80 and mainly involve getting the shifters and deraileurs adjusted properly. They'll also lubricate the chain and adjust the brakes.