Payment processing fees vary depending on the payment gateway, currency, and region. They are a necessary cost of doing business so are unavoidable. It is nice however to be able to choose who you do business with.
Here is a quick overview of popular payment gateways in AU dollars.
PayPal: 2.6% + $0.30 for transactions over $10
Stripe: 1.75% + $0.30 per transaction
Shopify Payments:  2.9% + 30¢ per transaction
Shopify Third Party (i.e. using PayPal or Stripe on Shopify): The payment gateway fees PLUS 2% additional fees paid to Shopify for each transaction. This means you could end up paying up to 5% of total transaction as payment processing charges.
So you can see the ability to use Stripe on it's own is a great way to keep gateway costs down in the long term.