In my experience, discounts are easier to come by around boat show periods. 30 months ago, I was quoted, for a Beta 25 at a basic price, delivered, ~£4.3K.
Best price was from the factory, but at possible expense of agents' support.
I'd expect a B20 to be ~£200-£250. less.
No knowledge of Yanmar, but I'd expect to pay a bit more.
Above price ignores items such as propeller, exhaust system etc. Also, shallow sump, large alternator, "waterproof" panel are not included.
When I got my Beta some time ago, as well as the 'boat show discount' I was able to negotiate the shallow sump and a specific control panel into the same price. So, I suggest asking for the boat show discount even if there's no boat show and going for enhanced alternator, switch panel, sump (if required), hi-rise exhaust etc. Negotiate direct with the factory sales people. I guess you should also try the dealer/fitter.
It's well worth shopping around. When I was looking to replace my old Volvo 2030 I got a quote from Beta expecting it to be very competitive. Actually, at the time, it was not as my local Volvo agent was offering a 25% discount on engine/saildrive packages. Instillation was also simpler being virtually slot out and slot in, and I was able to re-use my VP folding propeller. These offers seem seasonal, I'm not sure where we currently are in the annual cycle.
dated October 2013. I bought a 2YM15, having got a price of £3700 at the 2013 London Boat, rang them up in February/early March and they kept to the price. From the earlier thread the 2YM15's were over 5k then and that still seems to be the price. Perhaps there was a price hike in mid 2013 but the logic tells me I could get a 3YM20 for a little over 4k if I wait for the next time the discounting cycle comes around.