Spell Level times Caster Level times Item Type = Market Price.
In this case, Spell level 6, Caster level 11.
6x11 = 66.
So 66 times the price factor for the item type in question.
If it's a one-shot Rune (FRCS), that's 50gp, so 66x50gp means, 3300gp for a one-use Rune of Antimagic Field.
If it's a one-shot Contingent Spell (UE), that's 100gp, so 66x100gp means, 6600gp for a Contingent Antimagic Field.
A Rune (FRCS again) that can be used once per day, that's 400gp, so 66x400gp means, 26,400gp for a Rune of Antimagic Field 91/day).
For a Staff, it's 750gp; 66x750gp is 49,500gp, for a Staff of Antimagic Field with 50 charges.
Some other form of item, with 50 charges, that is command word activated, would be 900gp, 66x900gp is 59,400gp.
An unlimited-use version of that same widget would be 1,800gp; 66x1800 is 118,800gp.
If it's use-activated instead of command-word activated, a 50 charge item would be based on 1,000gp, and would cost 66,000gp.
That sort of use-activated item, with no limit to how often it functions, would use a 2000gp multiplier, for a cost of 132,000gp.
...
If any of the last four do NOT occupy a limited space, the costs double. For those with 50 charges, if the power requires 2 charges, that power is halved (the two modifiers could both apply, and effectively cancel each other out).
All that said ... an item that casts Antimagic Field without limit is VERY powerful, and probably deserves to just be banned from the get-go.
