It's bunk that people are saying that just because your child attends an "affluent" daycare that you should expect to have this expensive request. My kids go to public school, and this type of madness is there too. This week is their Teacher Appreciation week. I am TOLD by the room mothers and the PTA/PTO what to bring each day, how much to spend and at what stores. I am also requested to send in food for lunch and dinner all week, and to sign up to take the kids to lunch each day. It is RIDICULOUS! Why is this event a week long? Why can't it be one day? What other profession gets a whole week to be "appreciated"?
Now this all being said, I am a stay at home mom with the luxury of being able to volunteer regularly and almost always when asked. I spend no less than 10 hours per week at my children's schools. Therefore when this week rolls around, I do participate, however it is on my terms. Because I spend my time volunteering on a regular basis, I do what I want and will lovingly participate in the small, simple things like sweet notes from my child, a nice card from me and my husband, sweet treats, etc...
I look at these "demands" by room moms and PTO as the way for parents who work and cannot be in the schools volunteering to feel like they contribute. But this may not fly with them either given the state of our economy and that almost everyone is pinching pennies these days and cannot afford to spend $50+ on a teacher in a week.
Teacher Appreciation week is not my job or any parent's job to supplement a teacher's income. Don't like teacher pay? Don't become a teacher. Sorry to offend anyone, but that's how I see it.
So to answer your question, hell no it's not tacky not to give $20. And quite frankly from the discussions I've had with most teachers, they do NOT expect this. Give from your heart, not your wallet.