It's 11. The abilities of the creator are never considered in magic item DCs, for ease of use.
Magic items assume the caster had the minimum ability score necessary to cast the spell. Sleep is a 1st-level spell, so you only need INT 11 to cast it, which gives a DC of 11. 2nd-level spell items have DCs of 13 (10 + 2 from level + 1 from INT), 3rd-level is DC 14, 4th-level DC 16, and so on.
Ask your GM if you can invent an improved version that costs more.
You could maybe create it with Heighten Spell to use a higher level sleep spell. This has the advantage of treating it like whatever level you heighten it to, so if you heighten it to a 4th level spell the DC rises from 11 to 16.
This has the downside of changing the price to create it. A lot.
The math gets weird because this is a weapon (ammo) that usually uses a scaling price rather than a fixed price, so there is no easy formula on the pricing chart to guide us.
But can reverse-engineer the existing price of 132gp. For this, we assume the Sleep portion is fixed (it's not treated as a +1 bonus like Flaming or Bane).
When crafting ammo, you craft 50 items at a time, so 132x60 = 6,600gp base price to make 50 sleep arrows. the +1 portion is 2,000gp, so that leaves 4,600 for the sleep portion of the arrows.
The other prices on the chart all use the same basic formula: X * SL * CL where SL = spell level, CL = caster level, and X = some specific amount of GP. For these sleep arrows, we now have our formula: 4,600 * 1 * 1.
Finally, we plug our new variables for our heightened sleep arrows (4th level, requires a 7th level wizard) into that formula: 4,600 * 4 * 7 = 128,800 base price for a batch of 50, or 64,400gp to make them yourself.
Divide that by 50 for the individual price and we get 2,576 base price per 4th level sleep arrow, or 1,288 each to make them yourself (but you probably still have to make 50 at a time, per the normal crafting rules).
All of which makes a couple assumptions that your GM might not agree with so, as always when crafting custom items, make sure your GM approves.
You could maybe create it with Heighten Spell to use a higher level sleep spell. This has the advantage of treating it like whatever level you heighten it to, so if you heighten it to a 4th level spell the DC rises from 11 to 16.
This has the downside of changing the price to create it. A lot.
The math gets weird because this is a weapon (ammo) that usually uses a scaling price rather than a fixed price, so there is no easy formula on the pricing chart to guide us.
But can reverse-engineer the existing price of 132gp. For this, we assume the Sleep portion is fixed (it's not treated as a +1 bonus like Flaming or Bane).
When crafting ammo, you craft 50 items at a time, so 132x60 = 6,600gp base price to make 50 sleep arrows. the +1 portion is 2,000gp, so that leaves 4,600 for the sleep portion of the arrows.
The other prices on the chart all use the same basic formula: X * SL * CL where SL = spell level, CL = caster level, and X = some specific amount of GP. For these sleep arrows, we now have our formula: 4,600 * 1 * 1.
Finally, we plug our new variables for our heightened sleep arrows (4th level, requires a 7th level wizard) into that formula: 4,600 * 4 * 7 = 128,800 base price for a batch of 50, or 64,400gp to make them yourself.
Divide that by 50 for the individual price and we get 2,576 base price per 4th level sleep arrow, or 1,288 each to make them yourself (but you probably still have to make 50 at a time, per the normal crafting rules).
All of which makes a couple assumptions that your GM might not agree with so, as always when crafting custom items, make sure your GM approves.
50 masterwork arrows are 300 gp (actually 302.5), so that is 4300gp for the sleep.
The arrow is also at caster level 5, not 1. So the formula would be 4300 = X * 1 * 5, which works out to X = 860gp. So spell level (1) * caster level (5) * 860gp = 4300 gp.
Finally, we plug our new variables for our heightened sleep arrows (4th level, requires a 7th level wizard) into that formula: 4,600 * 4 * 7 = 128,800 base price for a batch of 50, or 64,400gp to make them yourself.
Using your method but my numbers, that would be spell level (4) * caster level (7) x 860 = 24,080 gp for 50 sleep arrows. Plus the 2,300 gp for the +1 arrow itself, for a total of 26,380 gp for 50 arrows or about 528gp individually.