Conference travel has been a major bonus for my family, because I can't leave them behind, either! (Last spring we went to the original Coronado, in CA on conference travel. It was cold

).
Ask any likely teenage or college age candidates if they would like to go. Advertising in your church bulletin might be a good way to find a potential babysitter if you don't know any- but I've never had trouble finding one. Spell out their duties, and your expectation for behavior, in writing so there won't be any hard feelings or misunderstandings. If they're under 18, obviously you are acting as her parent, so I'd be pretty clear on what she could and couldn't do even in the off hours. A curfew is fair at any age, because she will be waking you up if she comes in at 2am from Pleasure Island!
If they really are going to be watching the kids all the time, a small stipend might be fair- but if they have most nights off I doubt that would be needed. Be sure you buy their Disney pass, though. Also check their health insurance to see if it covers them while traveling.
I always tried to give the babysitter her own room, even if we ended up sleeping on the fold-out couch. I don't know what the rooms are like at Coronado Springs, maybe this isn't possible. This is the biggest headache, IMHO. We always rented condos or villas for this reason. However, it's a pain being offsite from the conference, you won't be able to drop by the pool and see the kids between lectures

.
Anyway, we have had such great times taking someone along when the kids were little- and if you want to ride Rockin' Rollercoaster, you can take turns with her instead of passing it up!