We have Cobra's. Make sure they have subchannels, the cheap ones with only 14 channels are useless. Ours are rechargeable, just stick them in the charger at the end of the day.I do suggest either rechargeable radios or batteries, otherwise you should buy stock in Energizer. Pick a channel-we use our anniversary date-but think of one or two alternates. If there is too much chatter, use an alternate. Realize this is public commication, there is no privacy(those with 'privacy features simply block you from hearing others conversation, they can stilll hear yours) so don't say anything you wouldn't want others to hear

No channel is 'private' or 'just for you', some people don't realize this and get very annoyed when someone else is on their channel. I suggest you turn them off in shows, or get ones with a vibrate feature. Many advertise a 2 or 5 mile range, these are best performance under ideal conditions. You will probably not get that at WDW, we never did. The worst reception for us was MK, yet we could sometimes get our party in MGM while we were in Epcot! They are not ideal, if you have cellphones without roaming charges they may work better. Still, they are definitely helpful. Dh would go for a snack while I searched for the best spot for Illuminations, would never find each other without the radios. We paid around 55 for our set of 2 radios with charger 2 years ago, and these were a decent quality set. You could get something that would well for 40-60 a set, possibly less. I would recommend sticking to Motorola or Cobra radios, do not go with ultra cheap noname brands.
I should clarify something though. The radios that offer the 2 mile range are what's called FRS radio, they are open to everyone and do not require a license to use. The ones that have a greater range use GMRS frequency and you ARE supposed to have license to use thos ranges. The package these come in should have information in them about the licensing. I believe it is $75 for 5 years. I've never really heard of them enforcing that rule on the walkie-talkies, but that is the law. I don't believe that most people are aware of this when they purchase the higher range radios.
Check here for the official rules.