I agree with Rogue, pay for a few yourself, at the end of the day you will only be paying 50% of their price as the rest will be going to you as a sponsor
It also enables you to gain visitors respect, if I read a review written by someone who actually had to dip their hand in their pocket I would believe it to be an honest review rather than someone who was given free access and the possibility that the review was a little biased.
If your budget doesn't stretch get a business partner on board but only as a last resort.