I know Hill-Rom has a program to help get someone a vest that can't afford it or doesn't have insurance to cover it. The other company's may do something like this as well. The Vest that HR will give you will likely be refurbished (used). It will come with all the warantees that a "new" vest will come with. Another option is Ebay but there would be no warantee and I wouldn't be surprised if the manufacturer refuses to work on it if it needs fixed.
I'm not sure if you have seen a Vest but the machine is the valuable part and doesn't get contaminated by use. The fabric vest jacket is a very inexpensive item and would never be redistributed used. I would never put one on that another cfer has used. In fact, when you get a Vest machine you can call the company and get new vest jackets as needed because they do become worn or crudy. Personally, I can't stand when the velcro gets all junked up...I just call and get a new one.
Are you in America? Do you have insurance? I bet you can get one. The studies have proven that it is a good purchase for insurance to cover because it saves them money in the long run through reduction in hospitalizations.