Granted you can find way cheaper ones, i just pulled the Ninja since I've always been a fan of their products.
Other than the filling station i'd recommend a scale; but its incredibly easy to do. If you have any questions feel free to PM me, I've played in the compressed gas business for years between paintball and home medical(O2)
You either need a tank with a diptube or you need to invert it since you need to fill it with liquid CO2, then as suggested you need the proper plumbing and a scale.
Since it's only $4-5 and it takes 5 minutes to get the tank filled at a sporting goods store that's what I do for mine. But to be fair I only use mine occasionally.
With only a 5lb tank, I'd think it would just be easier to get the paint ball tank filled when you get your 5lb tank filled. I went years getting my PB tank filled along with my 20lbs. I did recently get a fill sation and invert one of my tanks to fill the PB tank. It wasn't too difficult, but it is dangerious to mess around with compressed gasses.