Hi Linda,
Unfortunately, vacation rentals/short-term rentalsĀ are about that price. But if you figure how much hotel rooms would cost for a week for five people and the convenience of having a kitchen, etc. it works out to be a pretty good deal. Plus, you get to be in a real community not insulated in a hotel.
Long-term rentals are much cheaper. You can find homes for more like $500 a month. But that requires a commitment of several months to the owner.
I would suggest checking out Craigslist Costa Rica. You might find an individual owner willing to deal on a month-long rental. Of course, buyer beware just in the U.S. and make sure the rental is legit before money changes hands.