On the $100 cost part - you can purchase bits for your drill that allow you to sharpen the blades, or you can use a wheel grinder if you have one. Most lawnmower tune-ups focus on the carb, replacing hoses, the spark plug, and the air filter. You can easily get all those parts for ~$30 and DIY. The only thing you'll have to buy new (or used) are the wheels - I would consider looking for someone who buys and repairs old lawnmowers, they're bound to have some drive wheels in good condition.
Back to your original question, my lawnmower is 6 years old but I've had it for about a year and a half now. I bought it from someone who has a side-job landscaping business and his philosophy was to just run his mowers until they needed repair and then sell them. Honda mowers - the $600-$700 ones. I got mine for $100 because it ran wonky. It needed a new carb ($13 for a whole new carb on Amazon) and air filter. I also discovered that someone using it hit a rock which caused the crankshaft to bend. A few hours with a heavy hammer and I was able to bend it back just about straight.
Prior to the Honda, I had another ~6 year old mower. This one was the cheapest model they sold and I bought it for I think $40 off a guy who refubs them. Then a year and a half ago, the crankcase developed a stress fracture that caused it to leak lots of oil. Tried to use JB Weld with no success, so onto the curb it trod.