The Freedom Pro is your best bet if you want a foldable keyboard. I have not received mine yet but I needed one for a project and after some research it seemed the best still available. It is ~$100 at Amazon but if you google around you should be able to find a discount code for it. I picked mine up from wirelessground.com (15% coupon code mymobilegear).
Keep in mind there are no official drivers for it at this time however. KeyPro is available on the market but is $9.95 which might deter some. Also note I have never used keypro so can not say how well/poorly it performs.