Back-end donation-tracking solution for a small DIY website

What is the most efficient way to implement web-based customer/sales tracking for a small DIY website?

I’ve implemented a bare-bones HTML/JavaScript ecommerce-donation front end, using PayPal as the payment processor, and now I’m trying to figure out how to build the back end to track donors and what item they donated to.

My web host (Namecheap) runs MySQL, so my first thought is to create a custom database (a table each for Donors, Donations, and Items) and transfer data back and forth with client-side JavaScript. However, I know just enough about databases to know it’s a steep learning curve fraught with traps. If it’s the best way, fine, but there are other things I could do with those hours.

Tracking donors and items is similar to tracking customers and sales, so I’m wondering if there’s an off-the-shelf solution available with a friendly JavaScript-accessible API. I asked Namecheap Support, they don’t offer anything.

Googling turns up a bunch of CRMs (e.g. AgileCRM) but I can’t tell which ones have good APIs, or how much I’d have to pay. I have to think there’s a solution somewhere out there in the cloud that I can bend to work….anyone?

I’m not looking to add any graphics to my web page, I just need the back-end functionality: list donors’ email addresses, track donations, etc.