Okay, so here is what I have found out in my area (North DFW):
A 3k psi bottle (not sure cu. ft.) costs $95/year to rent and $300/fill, so that is $400 for one fill. At the price, I think this might be for a tall floor bottle, but don't quote me.
A 6k psi bottle (not sure cu. ft.) costs $95/year to rent and $425/fill, so that is $520 for one fill. At the price, I think this might be for a tall floor bottle, but don't quote me.
None of that includes a psi gauge, and high pressure fill hose assembly, which adds ~$204 on top of the rental and first fill. So unless you are filling a 2000 psi setup, you probably want a 6k psi setup, which means around $724 to get started.
A Nomad II portable compressor costs around $700 + shipping, and is designed to fill airguns only, not CF tanks. It can be run off of a car battery (by design). A disadvantage might be that you have to deal with moisture more than you would with nitrogen, and you can fill a CF tank from a nitrogen setup (for field use, if you don't want to haul the 6k bottle around).
I'll have to call back to find out the cu. ft. of the bottles to round this information out (sorry about that brain fart...I'm blaming "the media/wall/president/fake news").
Cheers,
Bucky