First, what's your site's url? There could be many more beta testers here that would be valuable. Also, what you're selling certainly guides how you want to go about handling this issue.

With that stated, generally, I'd say close the beta application process and let in the first x number of applications you got. Send each application a thank you note and tell them that you'll let them know once you've moved out of beta. You may piss off a few people here, but 100% of zero is still zero, so you're better off with the money.

That's my take, but again, background information would be nice.