re: Reasonable price for annual termite contract?

Unless the termite company did the pretreatment before the slab was poured and complete treatment when the house was finished, you are wasting money on a damage contract. There is no way to tell if termite damage is a few months old or a few years old. Termite companies will win that case 9 times out of 10. Sentricon isn't more effective than a liquid treatment such as Termidor, it's used more in situations where liquid treatments aren't possible such as very small crawl spaces that's aren't accessible.