Do you know of any keenly priced sources to get these built-in appliances?

It's worth shopping around and NOT buying all the same make, as the
performance and price of various integrated appliances varies wildly, with
some manufacturers being good at a particular thing. A careful perusal of
kelkoo should tell you all you need to know.

I ended up with an Ariston dishwasher, a Smeg 1600 washing machine and a
Bosch sensor dryer, as each appliance had the best price/performance ratio.
I found it was the dryer with the biggest markup over free standing like
with like. The dishwasher had the smallest differential over freestanding. I
bought it because I had a couple of previous similar Merloni models, which I
found to be excellent in operation. All appliances are 'AAA' rated.

Smeg WM: ~500
Bosch dryer: ~600
Ariston d/w: ~300

It was the dryer that really hurt, but it seems very difficult to source a
cheap condensing integrated dryer. However, I must say, it is really
excellent, much better than any free standing dryer I've used. The sensor
really works. The amount of water it collects in the tray is about 3-4 times
what my old one used to. The old one was drying after a 1200 spin instead of
a 1600 spin, too. The 1600 spin gets the clothes pretty dry to begin with.
I'll be plumbing it in soon, as I can't be bothered to empty the tray every
single time.

Christian.