Good question.
There's basically three schools of thought when it comes to pants: jeans, cargo pants, and classic poly/cotton work pants.
Me personally, I always liked jeans. They feel good, they last, and they're the cheapest option. For about $20 USD, you can pick up a pair of Levi's Carpenter Jeans at any Walmart. They're loose around the leg and seat, so you can climb and bend easily while wearing them, they have extra pockets and loops and things for tools, and they're little thinner than normal denim jeans so you don't die of heat exhaustion in the summer while being a little heavier than normal pants so you don't die of hypothermia in the winter. Jeans have saved me from splinters and things more times than I can count.
Some people prefer cargo pants, also called pocket pants or BDUs. I prefer Dickie's Canvas Tactical cargo pants, which are fairly long lasting and have all sorts of neat pockets and things. They should run you around $40-$50 USD in a uniform supply store or on Amazon. Other people swear by Carhartt or Duluth Trading Company, but most surveillance installers don't work on job sites with harsh enough conditions to justify the added expense and discomfort. I've worn Carhartt duck pants when working outdoors in terrible weather, and they were extremely warm, but that's literally the only nice thing I can think to say about them. They were much less flexible than my jeans.
Still, a lot of people love Carhartt duck pants (and coats, and jackets, and overalls). I used to wear a Carhartt duck jacket myself. Duck cargo pants from Carhartt should run you about $50 USD or so.
The third option is poly/cotton. The good thing about this option is that these pants are cheap and are essentially indestructible. The bad thing is everything else. They're uncomfortable, they don't breath, they don't bend or flex, they don't keep out the cold, they trap the heat, and they don't protect you from splinters or sparks. They also look dorky as hell. They're cheap, usually less than $10 USD a pair. I recommend Dickie's. Your mechanic probably wears these.
You can rent uniforms from places like Cintas, and they'll handle laundry and clothing repair. They'll also customize uniforms for you so that everybody looks the same. In my opinion, outfitting your workforce in a uniform makes you look more professional. A quick Google says that it usually costs $300-$350 per employee per year to set that up. If you do go this route, you'll get poly/cotton pants.
As far as shoes goes, a lot of people swear by Red Wings, but personally I never made enough money to afford fancy boots when I was an installer. Instead, I bought Caterpillar or Timberlands. Red Wings cost about $250 are said to last for ten years. Cats cost about $75 and Timbs cost about $100, and they both last about 3 years. This is the boots theory of economic unfairness.