one option would be to let your early users help you test things out for free.. with chargify, you can set up your site and everything in test mode, without paying for anything (I believe) as you work out the kinks. then you flip the switch to go from test to "live" when you feel you'll be able to cover the monthly fees.

Alternatively, you could do this, but charge your early customers via a simple Paypal recurring invoice until you're ready to turn on chargify.