What is a quarter from 1974 with no mint mark worth?

If there is no mint mark next to the tail of Washington's wig, it's possible that you have a filled-die error. That happens when grease or other material gets into the tiny recesses of a die and prevents metal from flowing in during the striking process. Unfortunately filled dies are fairly common so that error doesn't command more than a couple of bucks extra.

Check with a strong magnifying glass and see if there's any trace of the mint mark. Usually a filled-die error will leave a light image of whatever was supposed to be struck. If there's absolutely none, I'd suggest taking it to a coin expert for closer inspection to make sure that there isn't another cause. But without seeing the coin in person it's difficult to speculate further.