Let's face it, the true cost here is... time.
It's gonna take you a long time if you want a "true" old school.
All the current "old-school" servers out there (old-school my ass, if you ask me) are shitty and fail because simply "developers" rush everything, don't think things through (such as future economies, and the future of the server) and release their servers unfinished.
95% of the servers that are being released have no future because they simply add all their features from the beginning, which in return, gives the server no future, people get bored, and leave.
Also, like other people said before me, it could cost you nothing at all, but your time, if you just simply do it yourself.
However, if you decide to go the easy way and hire people to do it for you, I can assure you your server won't last you that long (if you are planning on going public, not private), simply because those people main focus is the cash they are getting, not the quality of the work they are doing for you.
My suggestion for you is to just start doing it yourself, jump ahead, do it, search, read guides (there are a shit-ton out there btw), even if the guide doesn't directly answer your question, usually the comments below it do, or at least hint things out for you.
Pick the hard way, it will always pay off for you (my personal life rule). Easy roads never work out.
