'93 Trek 1420 bike

Reasonable for whom?

Even high end bikes generally lose their value more rapidly than most people realize ...

• a very nice vintage bike with high end components MAY (but, probably not) appear to sell for a lot, but Dollar depreciation masks the loss in actual value ...
  

Some people would pay only $50 for a bike as old as your friend's ...

On the other hand, 'I' might pay many times that amount just for a frameset, alone (What do I know?!? Okay, it would have to be a steel frame of a doesn't-necessarily-have-to-be-great-but-does-have-to-be-recognizable heritage.) ...

In excellent condition, a non-descript 20 year old bike may only be worth 1/4th of its MSRP value ... possibly, less ...

So, $250-$300 is probably beyond reasonable ....

I suggest that if she is a REALLY close friend who is temporarily short on funds & you have extra money that you would like her to have without embarrassing her, then let your generosity be your guide ... figure that you would possibly be "gifting" her $100-to-150+.

On the other hand, you may not be able to find another bike in comparable condition for less in Sacramento-and-environs for less than $300 ... sometimes, used bikes which "fit" the rider are simply not readily available -- sometimes, SMALL frames warrant a premium over the "same" bike with a common frame size --sometimes not -- and so, $250-$300 might indeed be reasonable for both of you.