While I can't comment on cost since I'm not sure what the market is like over on your side of the world, I can tell you that at 300 hrs it's getting near the end of its life. Assuming it was maintained properly (ask for proof with receipts) it may still have a few seasons left in it no doubt. I think the average lifespan of a 4tec is around 400 hrs. I've seen them a lot higher and running great and I've seen them burnt up in less than 100. All in how it is taken care of. Id ask to take it for a test ride and do a compression check. Also check for any leaks (oil or coolant)
The money is ok. Being winter you can normally get it a but cheaper. But I they hold into it they will get more in the summer. You can easily get 400 or more hours on 4-tech engines that have had routine maintenance. Especially true with the smaller engines such as this one.
As I type this I see you are over the pond. Because if that, the money is right. They always cost more there.
Forgot to mention. At the VERY LEAST you MUST get a compression test. If you don't do this you could be buying an anchor. If at all possible you should test drive it as this will tell you many many things.