Front-end form for post submissions w/ lots of custom fields

I have someone I’m helping with their WordPress website. They’ve purchased the theme located here: https://gorillathemes.com/demo/smooth/

On the theme, there is the Submit Your Listing page (https://gorillathemes.com/demo/smooth/submit-your-listing/). The form on this page submits a new listing into the “Posts” area of WordPress for admin review. They also need the form to redirect to PayPal for payment before the submitted listing is approved.

With the theme, they recommend using Gravity Forms, which looks perfect. However, the person I’m working on the site for would like to avoid that cost. They’re not completely against it, but they want me to explore all other possible avenues first.

I’ve been having trouble finding other solutions that support all of the custom fields that the “add your listing” page has in the admin area of the theme. Mostly all I’ve found are plugins and methods for a simple front-end blog post submission (with title, body, and categories). And I have no idea how to build off of that.

I tried working with TDO Mini Forms, but I can’t figured out how to get custom fields added to the form, or how to get the form to just display on a page where I need it to (I can only get it to show in the sidebar). I have a feeling I may just be in need of a good tutorial, which I have not found.

I also found a method for hand coding a form with custom fields that will do what I want, but would like to leave that as my last-ditch approach. As it wouldn’t be very maintainable for someone with limited coding knowledge.

I’m mostly looking for suggestions on handling a front-end form that anyone can see and use, with lots of custom fields, and that puts the post in a “draft” state for admin approval. It also needs to redirect to PayPal for payment, but that’s something I can add on once the form is functioning.

Hopefully that all makes sense, and I appreciate the help.