03 Dropped a Valve

I have a 2003 Focus with the 2.0 SOHC engine. My me mechanic says he thinks it dropped a valve in the #3 cylinder. Is this common with these engines?

What are my options as far as repair vs replace?

Is replacing the engine a shade tree mechanic job or is it more involved?

I've had two 2.0 SOHC engines do this(2000 and 2002). One didn't drop the valve, the seat started moving around. When I heard the ticking start, I had the head re-done and it's been fine going on two years now. The other ,did drop the valve. It took out a piston and bent the rod.
If you can find an engine, swapping it out is not that bad.
Hope this helps.

I'm thinking it's probably a valve seat. My mechanic is going to pull the head to see if we can just put a new head on it. She wasn't driving when it happened so I'm hoping the damage is minimal.

Well, my mechanic pulled the head and she's toast. Tore the piston up pretty bad. Turned out to be a valve seat in cylinder 4.

Anyone have any recommendations on a good place to pick up an used engine that isn't going I cost an arm and a leg?

Picked up an engine today. The replacement has 79,000 miles on it, 50,000 less than what was on the car when we bought the car.