More detail needed. What does it mean, "convert to XML"?
"Export to IDML" 'converts' an entire InDesign document to XML format. That is the only way to convert an entire document to XML. Con: it's COMPLICATED. Pro: it's extremely complete.
"Export Tagged Text" creates sort of an XML file -- not really, but at least some software might work with it. Export to INX, CS-and-older precursor to IDML, looks more like properly formatted XML.
You can also manually tag any text and frame you like and use the "Export XML" command from the File menu (it seems to me somehow you managed to overlook that).
By way of *finale*: in my daily work I also have to export selected texts to XML. Since it's a complicated matter to git what you want, I shunned all of the above and wrote my own :) (only added this possibility for completeness' sake -- my exact procedure is not for sale).
when we send exported PDF documents to our digital magazine company they have to convert our pdf files from Indesign to XML, and they charge almost $4.00 per page to do this, which is very expensive. I would like to cut this cost and would like to do this, but we are not sure the procedure?
Can we just export the InDesign documents we have using the XML export that InDesign has?
Do you know *why* they convert their PDF to XML? Do you know what kind of XML they produce? You might not be aware of the fact that "XML" is a generic file format, kind of like an instruction to "save as image".
Returning to the "Probably not": to get anything useful out of your native InDesign file, you need to manually or semi-manually (depending on how "proper" the document was made) tag each and everything that should be included in the export. That takes time and expertise (but mostly time).