I bought a Burberry trench (classic one but slightly above the knee, not raglan sleeve which can be hard to wear) a few years ago and although it was eye wateringly expensive at the time (750 quid plus alteration) I have worn it so much and will wear it for years so the cost per wear will be lower than, for example, my mother, who mocks me for my expensive tastes but who will probably spend more on outerwear in 5-10 years and still not be satisfied. I love wearing it, the tailoring across the shoulder gives you a great line. It's just 'proper', if you know what I mean. You can also buy on eBay for cheaper (need to be careful about fugazzis though)
Check out TheSartorialist and Art of the Trench for ideas on how to wear them a thousand ways and how not to look mumsy.
Just something to consider. Coats from high street cost 100 plus and won't give nearly the longevity.