If you buy new before May 31st, you'll get the extra year of warranty, but unlikely to find any mowers "on sale." You will have an unlimited selection, as this time of the year, inventory levels are high and it is the height of the mower selling season. If you wait until late summer/early fall, you may find some returns/refurbs/floor models at a slightly discounted price, but the selection will be limited, and you'll won't get the extra year of warranty.
Paying a higher price only hurts once, but having a mower that is a compromise on features/performance lasts a lot longer. You may shop for a used one that matches your needs. Any remaining warranty stays with the mower. Send me the serial number and I can tell you if any warranty time is left on a specific unit.