ECommerce on WordPress

I run a small website design company. I have designed many websites but never an eCommerce site. I have a new client that runs a charity. The client wants the site to allow online contributions via credit card and wants a very small online store — just two products! The store would need shopping cart and checkout capability.

I have a basic knowledge of WordPress and have made a few custom themes.

How can I use WordPress to make online contributions and set up a small online store?

I am very busy and don’t want a steep learning curve for new software. I want this to be quick and easy.

Thanks in advance for any advice!