First- I didn't become a teacher for the little gifts I receive at the end of the year. They are always appreciated but never necessary.
Second- Don't look to spend a lot of money. Gift cards are nice. My favorites are to Barnes and Noble and Dunkin Donuts. Even in $5 denominations, they add up quickly.
Third- Go in with other parents (especially when you are in the upper grades when you have multiple teachers). About ten years ago, my homeroom gave me a baseball bat bag filled with wiffleballs and bats and then signed their names in fabric ink on the bag. Still have that bag and think of the kids when I see their names.
Fourth- Only give to the teachers that you appreciate. I had a parent stiff me many years ago, I wasn't upset, I thought the parent was irrational the whole year and wasn't expecting anything. I heard my colleagues got something cool from the parent. I wasn't jealous.
Lastly- Homemade gifts. Even just a note from a student that says thank you is more than enough for me. Again, I didn't become a teacher for the little gifts at the end of the year, but when you read a note from a child expressing their thanks for a job well done and sharing how they enjoyed spending the previous year with you...there cannot be a monetary amount placed on that.