
Imperium Knight |

At that low of level I would just use something like a gag in the prisoner's mouth and possible some sort of bindings that keep them from using their spells. Very few spells would work without somatic and verbal components plus no access to their spell components would handle most spell casters at low levels

Fuzzy-Wuzzy |

Manacles of Cooperation are only 2000 gp, which is about as cheap as a permanent magic item gets. But that may well be overkill, as Imperium Knight suggests.

Fuzzy-Wuzzy |

It's not that hard to make a concentration check. The charm would annoy the prisoner, but it would at best delay escape, not prevent it.
Are you specifically looking for something that works well enough that the authorities might reasonably use it but not well enough to keep the PCs prisoner? 'Cause that's a fine line to walk.

Bob Bob Bob |
It provides a +10 bonus to your Combat Maneuver Defense to keep from being disarmed in combat. Removing a weapon from a locked gauntlet or attaching a weapon to a locked gauntlet is a full-round action that provokes attacks of opportunity.
The price given is for a single locked gauntlet. The weight given applies only if you’re wearing a breastplate, light armor, or no armor. Otherwise, the locked gauntlet replaces a gauntlet you already have as part of the armor.
While the gauntlet is locked, you can’t use the hand wearing it for casting spells or employing skills. (You can still cast spells with somatic components, provided that your other hand is free.)
Like a normal gauntlet, a locked gauntlet lets you deal lethal damage rather than nonlethal damage with an unarmed strike.
That and a gag should cover all low-level spellcasters.

Kayerloth |
Blindfold, restrain, and gag them is going to put major inhibitions on most spellcasters. Obviously remove any spell component pouches or religious symbols or foci.
Hit them with a Status spell and now the authorities will know the direction and distance plus condition of their prisoner as long as they remain on the same plane of existence deterring escape and making recapture easier. Status is a 2nd level spell and lasts hours/caster level
Depending on what and how much is known about the caster might be worth simply getting their word not try and escape if they're known to be honorable etc.
Hostages depending on how 'nice' the authorities are and what sort of societal conditions exist.
Lack of sleep or periods of rest to memorize or change out existing spells.
Drug them so they do nothing but sleep and are hard to arouse or can't focus (i.e. ruin their ability to concentrate).
Guards trained to recognize spells and spellcasting efforts. (Give them a circumstance bonus to Spellcraft and/or Knowledge Arcana checks to recognize spells/spellcasting).

zainale |
cheapest way to detain and transport a spell caster.
things you will need
1. wad of cloth to stuff in the mouth of the spell caster.
2. something to wrap around the spell caster's mouth so it can not spit out the wad of cloth.
3. one blindfold. so they can't target anyone
4. a smelly sack to put over the spell caster's head.
5. one hammer to break all the spell caster's delicate finger. this does two things here. it prevents fancy finger waving and the pain ruins concentration.this is very important
6. rope for binding hands and feet and tying to a mount.
7. if it comes down to drugs. dose the prisoner's food/water. just keep them in a drugged stupor, while keeping all other steps in place.
8. keep them in minimal clothing preferably just their underwear to minimize hiding places.
all that should keep them well distracted while you transport them. then when you get to where you need to be you can heal their hands.

Derrick Winters |
Cheap version:
Hoodwink Cowl (75gp), blind & deaf
Straitjacket (5gp), grappled
Fetters (15gp), entangled & 1/2 speed
Manacles (15gp) restricted hands;
see Shackle for options how to use manacles
Manacle barbs (15gp each for manacles/fetters) Certain actions deal damage to the prisoner
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Alright; so for 140gp, we have a blind (no targeting) & deaf(20% failure for spells with verbal components, grappled(-4 dex, casting spells forces a DC 10+5+Spell level Concentration check), entangled(-4 dex, casting spells forces a DC 15+Spell level Concentration check) prisoner at 1/2 speed, who takes 1 damage if he
*uses more than 1 move action per turn
*attempts to move his legs
and take 1d4 dmg if he attempts to use a STR check to break his fetters/manacles.
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You can upgrade the manacles/fetters/straightjacket to masterwork if you want...
Using magical options, Bestow curse to reduce mental ability scores/inhibit actions with a 50% failure rate/inflict Spellblights and Insanity(Amnesia is best, because it locks away class abilities and most spellcasters gain their power from class levels)

Axoren |
Deal enough Int damage that they can no longer cast their spells.
If that doesn't give you enough time (they heal ability damage over time), you can use Bestow Curse twice:
Curse 1:
50% chance to do nothing on your turn.
Curse 2:
Spells take twice as long to cast. (not one of the recommended curses, but it's got about the same power as Curse 1)
Together, those two curses give you some reaction time to if they're going to cast a spell. They have a 50% chance to fail on turn 1, on turn 2 if they succeeded, they have another chance to fail again. That's a 75% chance to fail at casting a spell, with one turn to react, you can just beat the spellcaster in the face to make them fail for sure.
Stack nonlethal damage on top of them until they're unconscious and just hit them every so many hours to ensure they don't wake up.