When you say street lights , I assume that you are referring to illumination, lighting the streets, and not traffic signals, which are sometimes incorrectly called street lights.
As Leah mentioned, there are numerous factors that go into the cost of illumination. Type, size and location being the biggest influence on cost.
Normally, when building a roadway, the illumination cost is paid for as a lump sum price. This includes all costs associated with providing an illumination system, complete in place and functioning.
Below is a link to the Average Unit Price Index for the Idaho Transportation Department. These reports are put out every year and are very useful in estimating cost. You will not find Illumination in this report, though, because it varies so much from one project to the next.
Cost of street lights is a function of many things:
Location – light poles may cost more in, say, Miami than in Central Florida
Foundation Type – typical foundations are 5-8′ high, 3′ diameter cylinders that you can precast, and just drop in a hole that you auger, backfill, & attach the pole. If you have a utility conflict right below your pole, though, you’ll have to construct a spread footer. That adds materials and time, and will therefore increase your cost.
Pole height – the higher the pole, the more material goes into it, and the higher the cost will be. Typical light poles for roadways are between 40′-55′, though I’ve seen some that are as low as 22′.
Pole type – some areas want ornamental poles as opposed to the typical round-tube aluminum. The more ornate, the higher the cost.
Spec – some areas have high winds, and poles have to have thick enough walls to resist, say, 150mph wind loading. Others in central USA may be designed for wind speeds of 90mph. Thicker pole = more material = higher cost.
I’m no lighting expert, but the area average for street light poles down here in FL is anywhere from $3500 (for a 40′ pole) – $6000 (for a 50′ pole). Standard foundation, 150mph design wind speed, furnished and installed.
Keep in mind that doesn’t include electrical conduit & wiring to and from the pole, or any costs associated with the service point, or the cost to actually power the lighting.
This varies greatly depending on the type of light – . A good example of running cost is given here How much does it cost to run a street light? and an older, but more complete one in this FOI Request Street Lighting – Scottish Borders Council – answers quoted from that below:
1. I can confirm that there are 20,537 street lights in Scottish Borders Council area.
2. It cost £27.40 to power each street light in 2010.
3. The Council has spent £563,700 on electricity for street lights in 2010/11 to date.
4. It cost £334,142 to maintain/repair street lights in 2010/11 to date.
5. On average it costs £66 to maintain a street light for a year.
6. It cost £28.03 to power each street light in 2009.
7. In 2009/10 it cost £546,663 to power all of the Council’s street lights.
8. The maintenance costs of street lights in 2009/10 were £327,156.
9. The cost of running street lights in 2011 has risen.