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.
Free is an option. You could also slap a big "Or Buy This Better Thing" button generated by PayPal somewhere on the signup page. Thats a better option.
Why?
Because, its a great way to A/B test if what you're hoping to sell will get traction even with one person.
Set the expectation for payment early, Dan Martell wrote a solid post on why this has worked for him in the past. If you give it away free with no expectations of payment, it de-values your product. So set the expectation of payment, slap a "Buy This" button ont there.
I sold 6 tea kettles once before knowing where to get them myself. I sent an email to 3 saying sorry were out of stock (fairly true). Then I searched the web for kettle distributors. Sent the email to other 3 asking if its ok if they are a few weeks late. All 3 sold, and several dozen since then. All from a Buy Now Button on a landing page.
I worry about the scenario of building something that people are unwilling to pay for. Also the service can get rather resource-intensive so I can't afford many free users.
Alternatively, you could do this, but charge your early customers via a simple Paypal recurring invoice until you're ready to turn on chargify.