You aren't going to get better than Wordpress for that price. Closest options are Shopify and Squarespace. Both of them definitely not 0, with Shopify's starter coming in at around ~5 with the next jump up being 50/m, and Squarespace commerce at around ~20. Worth the price of admission for how much easier they are to use. The plus to both of these are that it's much easier to start adding different features to incentivize purchases and return customers.
If the price is seriously a concern, it's advisable instead to help your sister in law move away from a dedicated platform and instead utilize Etsy, Instagram (Shopping/Shops), and Gumroad to their advantages, and the cost there is 0 (until you sell things then they take a slice of the sale). Several reasons for this beyond cost, your sister in law is likely already using platforms like Instagram for social reach, and most people are going to trust platforms like Etsy over individual sites if they aren't built well. So more easy sales. Once she's grown past a certain stage she can then fully hire someone to manage a custom solution, but until then do not let her underestimate how great Etsy, Gumroad, etc are!
You aren't going to get better than Wordpress for that price. Closest options are Shopify and Squarespace. Both of them definitely not 0, with Shopify's starter coming in at around ~5 with the next jump up being 50/m, and Squarespace commerce at around ~20. Worth the price of admission for how much easier they are to use. The plus to both of these are that it's much easier to start adding different features to incentivize purchases and return customers.
If the price is seriously a concern, it's advisable instead to help your sister in law move away from a dedicated platform and instead utilize Etsy, Instagram (Shopping/Shops), and Gumroad to their advantages, and the cost there is 0 (until you sell things then they take a slice of the sale). Several reasons for this beyond cost, your sister in law is likely already using platforms like Instagram for social reach, and most people are going to trust platforms like Etsy over individual sites if they aren't built well. So more easy sales. Once she's grown past a certain stage she can then fully hire someone to manage a custom solution, but until then do not let her underestimate how great Etsy, Gumroad, etc are!