This, 100% this. CALL and negotiate for the best 'deal.'
I'm a local reseller for a few different manufacturers (but not the ones you're shopping for) and they all have the same rules for resellers-
MSRP (Manufacturer suggested retail price) which is the highest price you'll see listed for a particular item, almost never the asking price from a reseller but often referred to as 'originally $MSRP' with the asking price.
The MAP (minimum advertised price), generally the asking price and second half of the 'originally $MSRP, now $MAP!'
Lastly is the price the merchant actually pays for the item. If you call and negotiate you can most likely get a 'better deal' than the MAP, HOWEVER - remember this, those websites cost money, the payment processing services cost money, shipping costs money, time costs money, office space costs money, changing currencies costs money, everything costs money. Don't feel like you're entitled to a steep discount on ONE machine that will cost a seller time answering questions and troubleshooting at a distance.
I just sold a grinder to someone out of state. I don't stock the grinders, I had the manufacturer send it out. PayPal took $44.38 out of the total sale of $1520, just as an example. That was a nice chunk of my mark up. I'm sure there are slightly cheaper ways of getting paid, I don't sell to non-local customers often so it's not a priority for me. I also don't sell much often as I'm a local coffee roaster first and foremost.
Lastly- if possible go local, support for a specific brand of espresso machine locally makes that a MUCH more attractive purchase. This would be more important for the espresso machine as it is the thing that is more likely to need attention.
As for the best time to buy (the actual question posed!)- I dunno.
Personally I'm not afraid of refurbs / returns, if you're brave you could check 1st line and anyone else who actually stocks machines for them.