I have a 2007 SE Sedan DuraTech with ~90k miles. I got it with 4k miles on it so I am essentially the original owner. Well maintained and only repair unexpected by me was the engine mounts about 3k miles ago. It was a daily driver for me and now my daughter.
The DuraTech is a solid, long lasting engine. There are many reports of them lasting 200k miles. That said you are talking about a car with 142k miles on it and you have no idea how it was maintained. There are many parts other than an engine that can change a car from a good deal to a nightmare. What I would do is take it to a good mechanic to have a thorough inspection including a compression check, suspension inspection and a brake inspection. Even then I would count on spending $500 for routine and neglected maintenance, not including tires. I would count on spending $500 on any car with 142k miles on it, not just a DuraTech Focus.