Just so I can clarify my perspective: I am a horrible budgeter, I mean absolutely pathetic. I spend ludicrous amounts of money on my hobbies and toys (I'm anxiously awaiting my QX9650 as an upgrade to my QX6850 and working on purchasing my second pair of skis already this season). So money tends not to be an issue for me as long as I can somewhat justify it.
That being said: I hope you don't have to pay for it, because I certainly wouldn't. There's no reason to. There are plenty of open-source alternatives that add many more features and much greater security and stability. I would recommend using a Linux based samba share.