I help run fundraisers for the therapy riding program I volunteer at. Been doing it for years.
Bake sales work wonderfully. Don't set a price on things, say the price is a donation of their choosing. I have NEVER seen somebody get nasty and make off with several treats and only put in, lets say, a quarter. If anything, left to their own devices, people will put in more than they'd usually pay for their baked goods. I can't count how many times a friendly cowboy has ambled up to our table at the end of the night, stuck in a twenty, and taken one cookie with a smile and a wink.
Find somebody to sponsor an event, like barrels or something with cows. We do team sorting around here, and a friend of the program manager brings in his cows and its a whole lot of fun. Brings in the horsey people, too. It may be easier to set up a barrel event, however, if you don't know anyone with cows.
Raffles are great. We do five dollars a ticket, or five for twenty dollars. Whats raffled off is things like digital cameras, kindles, once a BBQ. Things like that are universal to the horse crowd and non-horse crowd alike.
If you have calm horses, or friends with calm horses, do pony rides. Always fun.
I have a boatload of other stuff we do, but I don't know what you want in specifics... I'm open to answering any questions, though!
Step one: Mount horse. Step two: Stay mounted.