I just found someone who will sell me an AS21 duel relief case in almost new condition, for $350 posted is this a good price?

Very good, you sometimes have to pay over $800 for a new mag case

So are they telling you it has standard bearings and never been machined???

Ha ha, I just noticed he says 'almost new condition'.......I'd say measure it or view it yourself and know what your looking at or don't pay over $200 for it and get a reputable specialist to check it out for you.