I am an independent contractor that contracts out to my interns that are spread around the whole country. I am still a small business that would like to make an efficient and affordable setup. So far, I have figured that for $500 a piece, I can buy pretty good refurbished PC from ebay and set up my software on them. What is the best bang for buck remote access I can deploy to have very smooth remote access system going on? I have read that windows RDP is a free option. Is there a exponentially better paid option that won't break the bank for me? What would you guys recommend?

Another reason I want to do this is that we don't have to deal with file transfer back and forth. I would like to keep the files in these computers. This bring me to my next question. Is it possible to set up a single drive that contains all the files and no matter whichever computer they have remoted in, they would save the files in one central location?