Make a new ACF Field Group (or edit an existing one) and add a suitably named number field:

https://www.screencast.com/t/yAx7H2x9OlVt

Assign that group to your custom post type:

https://www.screencast.com/t/kTH6PmMjypu

Then add some prices to some posts (see a note abut his later in this reply).

ACF fields are Post Meta field objects in the Form UI.

Note that, with fields made by ACF, when selecting the meta key, note a ‘gotcha’ with ACF ….

… it makes 3 meta keys per field, like this (in this example for a field named ‘land’):

#1 _land
#2 field_52f0fc4334f52
#3 land

In our Meta Key selection list, you need to use key #3, without the underscore at the start of the key name. If you choose #1 by mistake, in the field choices you will see the name of #2.

The fields will only show in the list if you have actually entered data in those fields inside posts and saved them. To define them alone without doing that, they will not show up, as our plugin does not look at the Field Group definitions, but at the actual data stored in the Post Meta table.