I've got twins in Kindergarten this year, and I'm the room mom for their class. I sent out a letter to the parents in the class (22 kids including my two) for them to participate in a gift card for the teacher if they wanted to. I suggested $5-10 max per student which would give us $110-220 total from the class if everyone participated. I'm figuring I'll easily get $150 or so based upon talking with other parents so far.
My girls are also giving her a monogrammed bag in her favorite colors (all of the teachers filled out a 'favorites' sheet for the PTA this year and the room moms got copies). I think the bag ended up being about $60 total.
For us, the fact that I'm no longer paying for their preschool means we actually have quite a bit of extra money every month compared to what I was paying last year. I typically send in a $25-30 gift card or gift of some kind every month (did a gift card to a local take out place at the beginning of school, a gift card to the local teacher supply store for Halloween, a gift basket from Costco for Thanksgiving, etc). Compared to $250 a month for their preschool, it's nothing really.
I also try to send in extras whenever they ask for specific supplies. Last week they were supposed to bring a box of candy canes for a project, so we sent 4 boxes. One week it was apples, so we sent in a whole bag of those. Next week it's brown paper bags. There are 2 or 3 children that for whatever reason just don't bring in stuff like that when it's requested, so I try to pick up the slack and give the teacher one less thing to think about.
For all of the office staff (principal, asst principal, secretary, receptionist, counselor, nurse) and all of their 'extra' teachers (art, music, PE, library, etc), we are doing movie bucket things. They had plastic popcorn containers at Target for $1. I'm going to put a $5 gift card to Blockbuster in it, along with microwave popcorn and some candy. I think I have 15 of those to do.
For all of the above, we include handmade cards telling each person what we appreciate most about them. If I didn't have any money to spend on gifts, I'd do the cards and try to do maybe a picture of my child in the card as well. Those are the things that I think teachers remember years and years later anyway.