I recommend for ongoing billing of both OASIS and 90 Minds that we look at Freshbooks. We can setup recurring bills and even integrate to payment processing via Paypay.
As we grow we need to offload as much administration as possible.
Essentially we can set this up for invoicing via email - have it automatically create renewals - and then forget about maintaining the info.
Cost for Freshbooks is $29.95/mo or $360/yr