If you just get a base color done, it should have been fairly inexpensive. Don't forget they also charge you to blowdry and style.
Once you get the base color done, touch ups are really cheap. At my spa they are $35 and up (and thats roots, grays, regrowth).
It will also help if when you book your next appointment with a new hairdresser, book extra time for a consult and tell her you just want your grays covered, match your natural color, and you only want to spend X. If the stylist is worth her weight and is a good colorist, she can make it happen.
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