Fun Playday Ideas?

So we are having out first ever Playday at our house! I used to go to playdays when I was little but haven't really gone to very many... here is what we have so far! Also does anyone have some good prize idea's that won't cost an arm and a leg? Also how much should we charge for people to be in the playday?

Barrel Racing
Pole Bending
Key Hole
Arena Race
Flag Race
Red Light Green Light
Egg in Spoon
Ride-a-Buck
Costume Contest
Musical Tubes (like musical chairs but with blow up tubes and you have to ride your horse around and when the music stops jump off your horse and put a foot in a tube)

Any other fun idea's???

Simon Says!
We played it at a local charity show... basically the same as the normal Simon says, but on horseback.

Apple/lolly bobbing! Ride up the end, get off, bob for apple/lolly, jump on, ride back. Can also be done with a lolly in a plate of flour.

Have a look here, list of games starts on page 19.

I thought of some more!
At one fun show, we had what they called a "water race" -- Everyone splits off into two teams, and each team has one horse. (Though I've also seen it done where everyone rides their own horse) Each team has two barrels at either end of the arena, and each barrel has a gallon ice cream bucket on top. The buckets closest to the gate are full of water, and the ones further away are empty.
The point of the game is that the first rider gets on the horse with a plastic cup, rides to the first barrel for their team, and scoops out some water. Then they have to run down to the other barrel, empty out their cup into the bucket, and run back to their team, where they hand off the horse and cup to the next rider. First team to fill their empty bucket wins.

Another one is the wheelbarrow race: There's a wheelbarrow at the far end of the arena, and two people ride in double on one horse. At the wheelbarrow, they both jump off, one gets in the wheelbarrow, and one pushes the wheelbarrow back out the gate while leading their horse.

There's also the Rescue Race and Monkey in the Tree.
Rescue Race has a barrel at the far end of the arena (like in plug). Everyone is in a two person team: one person goes out and stands by the barrel (or, if they're little kids, they can stand on the barrel), and the second person runs their horse in. The person by the barrel has to jump on the horse, and they ride double back to the gate.
Monkey in the Tree: A tire is suspended from a tree/crane/etc. in the center of the arena, and a barrel is at the far end. Two people ride in double to the tire, the second rider has to jump up and grab the tire and hang onto it while the first rider runs the horse down around the barrel, then runs back and picks up the person hanging from the tire.

Three legged sack race ias always fun too. One person waits, off the horse, down the other end holding the sack. The other riders rides up, jumps off, they both put one foot in the sack and run back leading horses.