actually you can even just get a normal PC to do file / folder sharing. it will be much cheaper than getting a server. but you do have to take note that you will need to do some backup towards the files inside the pc, unless you use RAID 1, 5 or etc….
my next question is how many people do you have in your company??
do you actually have a current network on your company side?
sorry for asking more questions than giving you ideas, but it will help me to give you more examples / help
I would recommend getting a small NAS appliance like from Buffalo Tech which would provide hard drive redudancy and better security controls.
try FreeNAS it will help you without extra cost..