A decade ago there were WordPress services were selling WordPress themes - customizing them was cumbersome and hence it was either using the theme as is with minimal UI changes or developing a new theme from scratch.

Since version 5.0 of WordPress in December 2018, it included a block-based editor named Gutenberg which allows users to customize the page's UI block-wise which can be worked upon by non-coders, and as a result, WordPress services started providing 'builder' services where one can customize a theme based on a builder's block HTML+CSS code within the admin instead of touching source files.

Here are a few of such famous 'builders' where which include starter kits (themes) if someone wants a jump start or else building one from scratch without necessarily touching a pre-made theme file.

I haven't used most of these - people I have associated with in the past, who are digital marketing gurus, use these extensively and got some feedback, so my reviews would be non-first-hand. Most of them have a trial, so please see which fits your requirement. If you are a freelancer or an agency then try going for the lifetime plan.

Elementor - most popular for a very long time - $59 a year per site - oldest in the market, famous for its ubiquitous drag-n-drop

WP Bakery - $56 for a single WordPress website

Elegant Themes - $89 a year OR $249 lifetime, both for unlimited sites

Kadence WP - $129 a year OR $699 lifetime, both for unlimited sites

WP Astra - starting at $47 a year OR $227 lifetime for unlimited sites

Brizy - $49 per year for a single WordPress website

Zion Builder - $39 for a single WordPress website OR $249 lifetime for unlimited sites - newest in the market, makes use of VueJS and claims to make the application and rank high on PageSpeed.

For WordPress, I recommend a combination of DigitalOcean and ServerPilot. DigitalOcean is a server service provider and ServerPilot is a 3rd-party cloud control panel for DigitalOcean. The most economical plan on DigitalOcean is $4 a month and a WordPress site on it via ServerPilot is $5.50 per month - it's actually $5 per DigitalOcean server and $0.50 per WordPress site, so it would be $9.50 per month for one WordPress site, $11.50 per month for 5 WordPress sites and $14 / mo for 10 WordPress sites.

The company behind ServerPilot has 2 WordPress products - datashuttle and heatshield - which are worth looking into for WordPress sites for your clients if they are seriously looking into security.