Stripe's API is reputably simple, and Stripe provides ready-made libraries to make your job even simpler. I can't imagine for a moment that using the ready-made library Stripe provides on Github takes more than an hour or two. So you're basically talking about a $10-50 job depending on how generous you feel when hiring an online code monkey or an adolescent down the street to do it for you.
Free + 2% might work for some non-technical user who wants to experiment with selling a product right now without investing a penny. It won't the moment the idea takes off. You'll immediately look for something with a monthly recurring fee.
The reason breaks down to psychology. When you sell a lot of stuff online, you only see the monthly recurring charge once. The transaction fees, by contrast, will be all over your statement. Sooner rather than later, you look at each and every single one, thinking: "Sigh, so much money being spent on this... Why am I paying for this again? Can't I use something else?"
As an anecdote to illustrate the point further: where I live, banks charge a tax on transactions, and what essentially amounts to a tax on paying that tax to boot. It's tiny - under .1%. But cash transactions are, as you'd expect, commonplace - including for things like buying houses.
At any rate, what I'm trying to get at here is that unless you're delivering something on top that is valuable enough to retain your users, you'll only be attracting users who are looking for a temporary solution to experiment with an idea. I'd expect them to churn the moment they see enough transactions that your extra fee associated with each one will prompt survey cheaper alternatives.
One such value, by the way, is having most if not all of the things you want to use in one place, or good APIs and integrations to be able to use the 3rd party tools you want. This matters a lot too in practice.
Maintaining and integrating several different poorly written self-hosted apps to run the cart, billing, delivery, affiliates, accounting, a few types of analytics, etc. is grueling. Integrating multiple hosted tools to do the same is also grueling - but less so, and it doesn't involve much maintenance. Being able to use new apps and services Zapier-or Segment-style is, by contrast, not grueling and extremely valuable.
Anyway, good luck with your project!
