Given that it is 2000 for a level 1 spell constant, I think it should be bumped up to at least that from sheer usefulness, even if your not getting the immune to summoned creatures/ac bonus [AC bonus would probably be along the lines of +4000/3 however, making it approx 3500 with everything but immune to summons, but +2 AC against only 3 alignments].

Even then, I would consider a price hike, but I'll leave that to the more experienced.