Air compressor for Geo Knight

Can anyone suggest a alternative to the air compressor sold along with the Geo Knight? They price it out at $650 for 7 gal, 1cfm,1000 psi, and 1/4" LINE.

From what I've read this compressor is loud and since I work out of a room in my home kinda of worried, mostly because much work will be done at night. I did read somewhere but can not find where, it mentioned some type of compressor and used CO2 cartridges, if I remember correctly. But did say was not only quieter but less expensive.

Any help with this is greatly appreciated.

THANKS,
Melissa