I'm making English Dogs badges right now!
I'd go between 50 and 100 quid, depending on leather and decoration quality and fit, as well as how much I like the design and how many there are. A one off is worth paying a bit more for.
Then again, decorating it yourself is like growing the mohawk - it's half the fun.
that might depend on where you decide to sell it, I've sold a few leather jackets at a friends motorcycle shop for around $100-$200 (only studed), and sold a few for rent money on eBay for upwards of $400 that were only half as good as yours (seriously, look on eBay, its pretty scary what people will pay for stuff)
a good way to find a fair price is to take the cost of materials and how many hours it took you to make it (pretend you were working over the counter for $10 per hour)
Have a look on ebay you can have your jacket done for £99 so you could add what ever the jacket cost to that.
Small world :)