Looking for O2 equipment advice

It is probably going to cost you roughly the same whichever way you go with it, so as dan stated, you need to decide what you want to do with the system. I overhauled my A-14 a few years ago, and it was in the ballpark of $6-700. You can certainly replace the mask with other surplus or new equipment, but should expect to spend $1-200 for a new high quality mask. I have found that some of the military masks can get painful on the bridge of your nose after wearing for a few hours, so that coupled with the A-14 sucking down O2 may drive you away from that route if you aren't searching for your double lennie.
Chris