The two most important of these factors, which affect cost, are the size of your property and the materials used. If you have a large yard, it will require more piping and additional sprinkler heads which will cause the price to rise. If you are worried about having a huge upfront cost, consider starting smaller with the initial plumbing and system, then gradually adding a couple of zones at a time.
The next factor that can affect cost is the quality of the piping, sprinkler heads, and timer system that you will use. Since sprinkler heads are the most active component and do most of the work, you will want to choose high quality ones to start. By investing in good quality parts initially, you will save money on maintenance and repairs in the long run.