Protecting trees? Dormant spray? (house, live, price)

[cynanthus]

How do all of you here in SF protect your trees from bugs and such? One of my neighbors told us that we need to use dormant spray every fall and spring, and insecticide every spring. We got a quote from a local tree service, and it's about $23/tree for dormant.

We live on 5 acres, with juniper, pinon, a few aspen and a few fruit trees. We were thinking of having about 30 trees -- those that surround the house -- sprayed.

Is that what everyone else does? Is $23/tree a decent price?