Ambrosia offers +2 to your saves (sacred bonus) against negative energy, energy drain and death effects for 1 hour. Costs 100 gp a piece.
The Dark Life Ring also offers +2 to your saves (profane instead of sacred) against channeled energy and inflict spells, and also reduces the damage by 5 points. Costs 1,250 gp a piece.
A Deathless armor enhacement reduces all damage taken from negative or positive energy by 10 points. Costs a +1 armor enhancement, which should be at least 4,000 gp.
The Scarab of Protection will grant Spell Resistance 20 and absorb 12 attacks that drains energy, death effects, or effects that cause negative energy damage, then it turns to dust. Cost is 38,000 gp and should be too high for a 4th level party, but it's worth mentioning.
To channel energy A cleric must be able to present her holy symbol (or unholy). So, anything you can come up with that prevents the cleric from presenting her holy symbol (and can convince your GM) can be used against her channel energy.
Iv had players throw a can of ink at a cleric that had his holy symbol painted on his shield so his holy symbol could no longer be recognized as such.
Others will attempt to Sunder or Steal the holy symbol, which will also prevent the cleric from using many of her cleric spells. But keep in mind that rarely a cleric walks on adventures with a single holy symbol.
Another solution is to apply the Pinned Condition on the cleric, which can be done after two rounds in a Grapple. This will severely limit her actions and will also prevent (most) of her spellcasting abilities.