you can check http://www.galls.com click on their clearance page.. sometimes they have good deals there. also look up Camp Safety West... they are out of Ohio but they also sometimes have used lights/sirens you can order for cheap.
Check out Powercallsirens.com......they have some nice siren boxes and as for lights check out strobesnmore.com....great lights with good prices...bought my strobes and a dash light from them.....Stay safe.......Paul
Check around at different sites. You will find a lot of them offer "package deals" where they may offer 2 or 4 strobes in a kit with the power supply. Sometimes they will cheap out on giving you a lower rated power supply that doesn't offer as many flash patterns for example as a more expensive, but if you can deal with that, that would be the way to go to start off. I started off with all used stuff, and proceeded to upgrade when I could afford to. Now I have a lot better setup, but the stuff I had in the beginning worked just as well. If you have a picture of your truck, or can provide us with more details on what you are looking for as far as level of lighting, maybe we can suggest certain lights. Here are a few sites to check out. I apologize for the repeats of what others have posted:
If anyone is interested in dash lights or sirens, I sell them. I can get anything you would like in any color. Just email me with what you would like and the color and I'll give you the price of my product. Also I have video of some of my product that you can email me and I can send to you. My email is firstname.lastname@example.org