For what you want to use it for, go for it for $300. Just for around home, I'd get one that you hook the hose up to and get as much pressure as I can pay for. You don't need a cadilac to drive to the store for groceries. 1200 psi is enough and 2000 psi would be the max to avoid tearing something up.
Bigger ones need more water volume to feed them which you may not supply through your garden hose. I've seen this little blue pressure washer for a little over a hundred bucks that would wash my car and deck just fine. Like the others said, you don't really want too much pressure on wood unless you are chipping paint. In fact I would recommend the spray can treatment for cleaning decks cause the high pressure is so messy.
I had heard not to wash mowers off with water cause it causes premature deck failure from rust. Just clean the big chunks off with a stick and get the wet grass off and leave the dried coating.