Have a family member with a small business that isn't looking to make huge changes to how they do things, but would be open to exploring a product to help them with invoicing and emailing invoices to customers. It would be nice if they could email the invoices, print the invoices and mail them if the customer wanted, or track in person sales if they wanted to do that.

Anyone have any recommendations, pros/cons or information on fees? They'd probably be willing to do some flat fee per month, but I think might take issue with a model charging a large percentage per paid invoice. Pretty easy to compare the flat fee per month across companies, but a bit more difficult to find if certain companies are charging a large difference in % of invoice for bank transfer, credit card use, etc.

Quickbooks seems to have a lot of features that they might could grow into over the years, but I don't think they'd start using almost any of these features day 1. There's also Stripe, Square, Zoho, Freshbooks, Xero, etc.

Would appreciate any and all input. Thanks!

Basic Quickbooks is around $30/month.... I'd start there. Very easy to set up & email invoices, run P&L, send statements etc.

I'd also recommend Basic Quickbooks.
It's a good app, and I've been using it for some time, too.
And now, when it comes to business, there are so many different software, apps, and other things that can help you. But sometimes, there is a need for custom software because each business has some specifics, and creating something from scratch may be the perfect solution. Here is the company's website: https://ddi-dev.com/. I worked with it some time ago, and it provided me with the perfect software for my business. All my requirements have been taken into account, and on the site, you can also check case studies, which will prove quality.