Other Parents Volunteering Me to Buy Gift for Coach

You are not obligated at all and even thought people mean well by this type of thing they often don't consider that even an extra $10 or $20 is a lot for a lot of families. I'd find the organizer and tell her that you apprecaite your efforts and you'd love to pick up the card or help some other way, but extra money is really tight right now. Or I think you can just mention to her that you and your daughter already have planned on thanking the coach in an individual way from your family and your daughter can wirte her a nice note or make here a picture or craft. I think that's a great alternative and should be completely respected by the other parents. You should 100% bring your daughter to her game - the first priority her is to allow her the joy and fun that comes with her playing soccer! Please don't feel embarassed at all!!

I would just tell the organizer that you already have something for the coach and bring the card you plan on giving. Have your child write something they like about the coach in it. That would mean more to me than $10.

There really is no issue here. The mom organizing this is truly trying to do something nice for the coach. I don't think there is any negligence on her part, other than considering others finances. I would email her back and tell her you already have something for the coach so you won't be participating. This will likely happen many more times over the years, so come up with a standard answer now and you won't have to feel put on the spot in the future.

There is no obligation for you to chip in for a gift! And don't let others expectation of you keep you from attending! I would just go, not mention the money thing and if you are approached just say that you are giving a personal thank you. They do not need to know that your personal thank you is in the form of a card! It's not bad manners at all to decline!
I have organized these things in the past and would hate for anyone to feel obligated. Even if people have not been able to give I ALWAYS include their name on the card! Not giving money doesn't mean that you are any less thankful for the coach.
You can just do what is right for you and your family! Don't ever be embarrassed for putting your family's needs first!

the e-mail should have been worded better... somehting like we are chipping in to get the couch a small gift. If you can throw in a few bucks great but not neccasary. We will also have a card for everyone to sign!

You do not have to give money, if a parent apporaches you about it say we are really tight on money and we can not spare any. Maybe offer to pick up the card, only if you really want to. Anything else they say to you just let it roll off, they mean well but obviously do not know how to go about it correctly.