Volunteer Nursing--need advice!

Hey all-

I'm an RN working in the USA (I'm from here). I am very interested in volunteer nursing opportunities overseas. However, there are many companies with a wide price range. I was wondering if anyone has had a awesome experience with a certain company or knows others that have and could make a recommendation? Or companies to avoid? Also looking for any tips anyone could offer such as what other steps to take prior to applying or once accepted, good ways to raise money, or about how much I should expect this to cost? Any help is appreciated!