OEM electronic signature solutions

Can anyone recommend a reliable and “cost effective” electronic signature provider which can be easily integrated into a Saas platform? We have briefly looked into options such as Adobe Echosign and some others but the pricing model does not seem to be Saas friendly and am hoping there are alternatives out there with a good API and appealing pricing models?

One of my clients had a similar need a couple years ago when HelloSign was just starting out. I can’t speak for them now, but they did have a fairly comprehensive API, multiple signing methods, and a very responsive support team.