Have you ever been a bridesmaid? Now honestly, how many times did you wear a bridesmaid dress again?
I have one bridesmaid dress that I never wore again and then as maid of honor at my sister's wedding I re-wore that skirt and top as a bridesmaid at a friend's wedding. But actually I just wore it for the photos because we didn't walk down the aisle. After formal portraits I changed into a different dress I had fallen in love with at a vintage store a week before the wedding -- with the bride's permission of course.
Anyway, the point is that I never wore these dresses again and you probably won't wear any of the bridesmaid dresses you've had to wear again either.
Did you get a gift that went with the dress like a necklace or earrings? If you're never wearing the dress again when will you wear the accessories?
My point is that when shopping for bridesmaid gifts treat each of your bridesmaids to a meaningful and personal gift. You don't have to get them all the same thing. And like a wedding favor it's better to put your money into something that your friends will use and enjoy.
And as for how much to spend on bridesmaid gifts that's up to you. If you're buying each girl something that she will truly enjoy I'm sure they won't compare notes behind your back and guess how much each item cost because they'll be so touched that you spent time thinking about getting them something special and not some token gift that either matches their never to be worn again bridesmaid dress or is some generic bridesmaid gift item they saw in the back of a bridal magazine.