I think any cheap sump pump should work fine.

You need to take into consideration the head (vertical distance between the pond and the tank), too. Pumps will have this information with them, usually on the metal info tag or in the manual. I concur with Cole Robbie that a sump pump is a good choice as long as it is rated to pump your required head - if not it will run slowly and in extremis can ruin the pump. Another option is a shallow well pump. You would not need a big one and there are all-in-one units that have a pressure tank built in the unit that should run between $200-$300. Fasten it to a piece of plywood so it does not vibrate all over the place and plumb with unions on the suction and discharge sides to it can be easily disconnected and brought in before the winter. Another advantage is that with a pressure reducer you can use it to run drip tape,

Tom