Use Paypal & E-junkie for your first few months and sell folks lifetime subscriptions to your service. $5 a month for e-junkie (not strictly necessary but it will save you a few hours of integration work), ~3% for Paypal.
After you've got a better handle on your market, have traction, and have passionate paying customers singing your praises, switch to a subscription billing provider and grandfather in the old users at free for life.
This assumes that you have nearly zero marginal cost per account, or a growth curve which can absorb the early adopters as a cost of doing business.
My only concern about this would be selling lifetime subscriptions for an embryonic service. What if it fails? This may be built into the terms, but it could also sour customers on your future offerings (or hurt your personal brand).
Otherwise, this seems like a good strategy for testing the waters with a new product.
My own view on "lifetime" anything is that I'm taking a gamble on whose lifetime is longer, and consider that when choosing that option. Ultimately, the amount I pay comes down to how long I think the company/product will last.
After you've got a better handle on your market, have traction, and have passionate paying customers singing your praises, switch to a subscription billing provider and grandfather in the old users at free for life.
This assumes that you have nearly zero marginal cost per account, or a growth curve which can absorb the early adopters as a cost of doing business.