I wouldn't expect much of a deal from any motorbike dealer. Still less on a Duke. Partly this is due to competition (or lack thereof), partly volume and partly to a poor approach to retail.
Taking your Ford example, Ford has over 130 main dealers in the UK, and between them they shift over 6,000 Fiestas PER MONTH.
KTM has 26 dealers in the UK (including IoM and NI), and they shift a bit over 6,000 bikes PER YEAR across KTM's entire range.
There's very little incentive for a dealer to talk discounts or sweeteners unless they seriously think you're cross-shopping against another brand or model. And even then, the Duke 390 is still in relatively high demand, so it's not like it'll be sitting around for long if they don't sell it to the first person who comes along.
Add to this a very traditional "spare-parts" approach to retailing (as in "Here's your widget, that's the price, do you want it or not?") and it can be really hard work to get anything extra when you buy a niche bike like the Duke.
Probably worth a try though.