I like the way you're thinking (smaller is better). I remember in the late 80s / early 90s a local top-40 in Tulsa doing "free music weekends." All weekend long we'd have chances to win the latest cassette from fill-in-the-flavor-of-the-week artist. The contest was, "caller #7 wins now!" The playback was a heavily scripted winner card that played back over the intro of the next song. In and out and gone.
People who listened for prizes loved it because we gave away a tape every couple of hours around the clock, people who loved the artists loved getting the tapes, and those who didn't like prizes could blink and miss it.
Now, everything's $100,000 for the name drawn at random from the names registered over the past three months of people who made it to one of our events and knew the winning phrase... it's just exhausting, for the listener and for the contest player.
One of the WORST contests I ever heard was in the mid-80s when a station did "Win A Hundred." You had to guess the entire serial note, and you had to keep track of previous right and wrong answers... $100 could take a week to win. It was TORTURE, and having a guess on the air (especially as more right letters were guessed) shut the entire station down. Misery for the staff, the listeners, and those playing.
Are you Q92? Give away $92 every hour during the workday, or at lunch. Make it about winning, not about changing somebody's life forever. Give away chocolate boxes on Valentine's Day. As was suggested above, know the demo of the contest and know the audience. Make it fast as well as fun. As the old adage says, it's not the prize of the gift, it's the thought that counts.