It does not take a lot of money - there are a couple free emulators available. You would need to have an Internet-connected server with a reasonably fast connection. How fast depends on how many users would be on the server.
If you are talking about doing this simply for the fun of flying anywhere then you could setup a local server (on your LAN) and serve from there, but without redirecting Internet traffic to that computer, no one outside the LAN will be able to connect.
A server could be as cheap as $15/mo on a basic cloud account if you're just talking about serving to a couple users.
Ramping up will take pretty significant time though, all of the server emulators I know of run on old versions of Aion. To the best of my knowledge this means that everyone connecting to the private server must have the appropriate game version installed.
[Only registered and activated users can see links. Click Here To Register...] appears to be the "best" option and runs 2.7-3.0, but development has been inactive for ~6-9 months.
Emulating all game conditions, environments, monsters, etc can be challenging so emulators are not simple beasts.
Through all of this, the point is really being missed though... if you're going to play on a local/private server then you could just edit your character's inventory in the server's database and have whatever item you wanted from the boss you talk about flying directly to.
If you think private servers don't have enough people but you want to do dungeons and get gear, why not play on NCSoft/retail?
P.S. Is your avatar from the '70s lol?