a used mim strat will range in value from about $250 for a standard to 500 for a jimmy vaughn. classic series should get you 3-400.
The problem is that strats are falling out of favor and are probably the most sold model of guitar in history so the used inventory is huge. It's not hard to throw a rock and hit a decent strat for sale. I will say that special transcendent strats seem to be some of the hardest guitars to find though- they are very inconsistent from guitar to guitar.