What is your tank labeled with? most won't do another company's tank. If your tank says "Airgas" you have to take it to them, if it says "Praxair" you have to take it to them etc.
I just got more C25 this week from airgas. Tax and everything I was $152.00
You will have to wait a few days.
I considered a backup tank, but the fact that airgas will swap it so quickly, I couldn't justify the expense. plus my tank is the big one, and it usually lasts me a few months in my garage