Your provider should have a price list. In my experience, the price lists are usually numberprefix, cost. But sometimes cost depends on actual carrier, not original carrier, so you can't know the price until a porting lookup is made, and those cost money too (those are generally a usage tiered $/lookup, starts around 0.01USD at low usage, but can go much lower if you have volume)

Yeah! Just send an SMS, then check your telco account and it'll tell you the price /s