The more important question is whether you will have the subpoena correctly issue. You may want to seek counsel from an attorney on doing so.
As far as costs, you likely will not have to pay for that witness to appear.
Place all potential witnesses under subpoena, and once you do, you will place them under the court's power to demand their presence in court. I suggest you not do this yourself, hire an attorney to help you, because mistakes in litigation can be costly.
I often take cases other attorneys won't, so call me for a free consultation. My number is 727-712-3333, or you can view my website at www.TampaConsumerLawyer.com