Thank you for contacting us and I'd be happy to assist.
Based on the requirements that you've shared, here is the structure that I'll recommend:
1. You'll have the custom post type "House renovation Estimate" which will be in a one-to-many relationship with the main post type "House".
Note: A better name for this custom post type would be "House Renovation Estimate Item", as each post in this will represent a single expense item and not all the records.
2. There will be two custom taxonomies, attached to this post type:
This taxonomy will hold options/terms for the main categories of expense types, for example, "Electrical", "Plumbing", "Fees" etc.
b). Renovation Item
This taxonomy will hold options/terms for the actual individual expense items, for example, "doorbell system", "stove/dryer", "lights" etc.
Using taxonomy for this will make it easy for the user to select from the pre-entered options, rather than having to enter all options manually. And user can always add more terms to this, in case a relevant one doesn't already exist.
3. You can then add two number-type custom fields to this post type, one for the lower-cost price range and the other for the upper-cost price range.
Through this structure, it will be easy to add and maintain a record of each expense item, related to an individual house, through the front-end form.
I hope this helps and please let me know if you need any further assistance with this.