You don't give us the exact model numbers for the unit or engine, so I am making some assumptions as to parts. You must have a copy of the bill, breaking down parts and labor. Here is how I see it, realize that my labor rate is just a guess for your area. Three blades would cost $20-30. Air filter would be $25-40. Oil filter would be $10-15. Two quarts of oil would be $3.50-5.00 qt. Forty five minutes of labor at $100/hr. Parts would be $102-155. Differences in prices depends on exact part and whether OEM or aftermarket parts are used. Labor would be $75. Using this figures gives us a total bill of $177-230+ tax. Doesn't really look that far out of line. I used forty five minutes because you would have to be a great mechanic and everything would have to go perfectly to get done in thirty minutes. I'll bet it took them close to an hour to do the job. As IL said, I'll bet if they are a good shop they did a quick once over, plus scraped the deck before installing new blades. If you do it yourself, time it. This might be the way it goes. Start timer. 1. Starter unit and bring to the garage. 2. While warming up the engine, gather all your needed tools and parts in a neutral area. 2. Engine warm, bring in unit and drain oil. While oil is draining, remove and replace oil and air filters. 3. Fill with fresh oil and run, then double check and top off. 4. Get out the jack and raise the unit. 5. Remove the blades (hope you have air tools or a good electric impact as those nuts are on tight) and clean the underside of the deck. 6. Install new blades and grease spindles. Stop the timer. Do you still feel that you could do it in less than 30 minutes. Now let's include things I did not include in the timed sequence. Taking the time to look up parts and getting them from stock. Taking extra time to double check my work, so I'm sure it is done right. Moving your piece of equipment out of and back to holding area. Time needed to right up the work order. Always giving the unit a quick safety and defective part checkover. I have to protect myself from the guy who had his unit in for an engine tune-up and two weeks later has a drive belt break, then claiming I should have seen it was bad. Again, I say these are just guesses as I am not in your area, but at least now you can see the work order from the dealers side of view. Did he overcharge you? Only you can decide that after reviewing your bill and what I just posted.