Need help with plugin/something

Hello I’m developing a website for our church. And one of the need is to have a online giving page. My goal is something like this

https://postimg.org/image/q7td6uh71/

So far I have this done.

https://postimg.org/image/kj8a2k0b1/

website link is

stage.iwcentre.com

So far my forms can make a total, but I don’t know how to link the submit button to paypal. Ninja form has Paypal express add-on but it’s kinda expensive. I want to know if there’s an alternative for that and I’m hoping not to use paypal express but the regular paypal if possbile?

Thanks in advance!