Ace - As you said, the area sets the rates. While I am not in a large metro area like NYC, Chicago, DFW, etc. we are still able to charge $55 - 65.00/hr.and we are a city of around 250000 pop. Check and see what plumbers charge for their service calls. People still don't treat irrigators as professionals yet, so sometimes it is hard to get their rates, but you can get close. Don't sell yourself short even if you don't know a whole lot yet. After all you are trying to repair their irrigation system - research and troubleshooting are all billable tasks. I'd be willing to bet that all of these old, grey-headed, mossy horned, repair techs have ran into a problem or two that they couldn't puzzle out, and had to make a phone call or two to get the answers. And you can bet your butt that the time on the phone with whomever was also time on the clock. They were getting paid for learning too. Keep in mind it is a lot harder to raise rates later after you have been busy around town, because people talk - "That Ace is really good on sprinklers, and he only charged me $25.00/hr."
As for parts, it depends on where you buy them. If you are buying from a supply house, and you should be, they usually have a discount of 30-40% off of suggested list price. We charge retail list price to the customers. If you are forced to buy from the Box stores (HD, Lowes, etc.) you have to remember that the customer can buy them at the same price you do. But you still have to mark up the products to make a profit and to cover your time to pick them up etc. It is not unreasonable to work on a 25% GP on those parts. Take the price you paid and divide it by .75 to arrive at a selling price. ie-Item costs you $10.00 divided by .75 = $13.33 selling price. That will give you a true 25% gross profit.
Make the money on the parts, and you can also stand to increase the prices a bit. The market will tell you when you're getting out of line.
Just some thoughts from my way,
Jerry