Hi Freyr,
I interpret the last sentence of FAR 52.217-7 to indicate delivery speed, not price. For instance, if your base CLINS are required to be delivered 30 days ARO, then your option CLINS would generally be required to be delivered within 30 days after the contractor received the exercised option - unless you agreed to something else. You could also think of it in context of something that is supposed to be delivered in multiple shipments and a specified rate (i.e. 5 ea/month for 6 months).
Either way, I think I would use something more along the lines of FAR 52.217-9 in your scenario. You can set the number of days for the advanced notice and the exercise of the option at whatever you need, but I would just be conscious of how much notice a contractor might need to adjust their manpower or cleaning supplies. If they're going to need to order anything special for that optional service, more advanced notice might be warranted. If its just a matter of cleaning an additional small area, maybe 1-2 days notice is all that's needed.
The beauty of all the option provisions and clauses prescribed by FAR 17.208 is that they are all "substantially the same as...". Maybe this is an opportunity to write something that fits your situation better than the standard clauses.