Your not married yet and already fighting over money? That's not a good sign.
I'm frugal and $20 is cheap. These people are participating in an important event in your life. How much are they spending to participate? The dress, the shoes, the nylons, the hair, etc.
When we got married, we bought the women in our wedding party a gold necklace - granted, we only had two bridesmaids and two groomsmen (this was the second for both of us). The men were given gold tie clasps and cuff links. I think they were $100 each. Since we were buying in "bulk" our jeweler gave us a discount.
When my husband was best man in a wedding years ago - each groomsman was given a Lands End travel bag with their names/initials embroidered and toiletry bag - that's been 20+ years and my husband STILL uses them.
Personalized gifts will mean more. At least to me they would.
I'm concerned though that you are already fighting over money. Seriously, not a good sign. If it were my wedding? $50 would be the cheap end. I have friend that does the gifts for large corporations...if you would like, i can find out if he does small events like this. PM me if you are interested.