Hi Caroline,
Price, under which initial inquiry was made will always be the final price for that booking unless you change it manually under the special offer feature.
In my experience the most important thing is to keep your potential guests aware of might be changes in price so what I would do in your situation is make a special offer matching your required price under that inquiry and if guest is happy he should accepts it so VOILA 🙂
Just be aware that under special offer there is no automatic addition of your extra charges like extra person, cleaning etc.
Hope that helps.
Kind regards,
Natalija