I mean, the thing with the power conversion is not the voltage (as every house in the US has 240v going into it anyway), it's the hertz. The rest-of-the-world had a wrong opinion and thought 50Hz was a good idea, and we wisely chose 60Hz. Depending ENTIRELY on what electronics might be onboard that vacuum cleaner, it may or may not matter. If it's a typical 'universal' (AC/DC) motor, 240V at 60Hz should work just fine. If it's... literally anything else, you might have a problem. It's an older vac, though, so I'd imagine it should have a normal universal motor and no electronic gadgetry. Though if it did have any computers on board, those would likely be fine, too, because they rectify the AC to DC power anyway.
Wiring a 240v outlet would be a piece of cake for anybody who knows their way around a breaker box. You could legit just install a 240v outlet right next to the breaker box and make a special extension cord long enough to reach your vacuuming grounds. (I personally wouldn't use a 120v outlet with a 120v extension cord, because I know somebody else would inevitably wind up plugging something else into it.) Add a $2 plug converter to convert to UK or EU plug, and that all in would be way cheaper than buying a $200 step-up converter. Or, like Miles said, you could make a plug adapter (maybe pigtail style) for a dryer, stove, or even window A/C plug, if you have one of those handy.
