I am not much of a bike mechanic, but I do know those are V Brakes. It shouldn't cost much to replace, and frankly, I would pay a bike shop to do it. My son once broke his front V Brake and if I remember correctly, the bike shop replaced the assembly while we waited, and it didn't cost much, maybe $20 including labor.

Edit:
Maybe the v brakes on your Trek are better quality than the ones I put on my son's Trek, but I doubt it. I just Googled the standard V Brake for your Trek and it appears to be a Tektro V Brake that you can get for, maybe $12.