Here's some guidance for buying the right product. Measure the height of bushes and the height of the sections of any trees you want to light. For trees and bushes, figure on about 50 lights per foot of height, or double that number if you're using miniature lights. Look for light strings that can be plugged into each other, especially if you are using chasing lights. Keep an eye out for sales.
Many stores compete with each other to have the lowest prices.
Hire an electrician to install an outlet or two in your eaves. Make sure to have the electrician put the outlets on a switch so you don't have to unplug the lights to turn them off. Consider putting your lights on a timer if possible. Pick up great deals for next year during the after-Christmas sales. Make sure the model of lights you buy has not been recalled.