I would think that initial prices would be a little higher than the standard model P99s just because they are a new thing and people will want them. But as demand drops they will probably settle to around the $600 mark.
What kind of M1A do you have? I just ordered a SA Std M1A in .308 Win - picking it up next Thurs!
I'm also a member of BattleRifles - same handle on that forum.