Ask HN: Online Payment for SaaS Startup

Hello Community, we are four guys building a SaaS-Plattform that makes customer feedback for small companies (hotels, gastronomy, catering, etc.) really easy. Its somewhat similiar to talkbin and Skweal. My question is: which online payment solution would you recommend for a startup that is selling an SaaS solution?

A lot of startups could benefit from a discussion on this top. I read some articles and found some nice links, for example http://stackoverflow.com/questions/2556/whats-the-best-online-payment-processing-solution. But I guess in the end it comes down to low monthly costs, easy to integrate and easy process for our customers. It would be really nice if someone could give me some insights oder point to a good blogpost about it.

Here are some additional information: As of now every potential customer (a hotel manager for example) has to talk to us, and if he es interested we send him his account and a bill. But we obviously like to implement an online payment process, so that customers can pay for our product on our website. Our product is kinda high volume, low value, so we dont expect payments above 1.000 Euros per transaction. (As of now it is more like low volume, low value...) This is our current website (in german): www.honestly.de but we are working on a relaunch right now.