Question about torch bottles

[Rhino]

I've finally gotten sick of not having a torch around. I purchased one at auction yesterday with a full set of bottles and cart. I know I can have them refilled, but what is the certification process and how much does it cost? How often does a tank need to be recertified? Would it be more cost beneficial to find a place willing to do a cylinder exchange?

I've used a torch for decades, but It's strange that I never really put much thought into the tanks until now.