I will be going to Bali and I want to bring a vacuum cleaner worth less than 250 USD. Do I need to declare it? Will I need to pay import taxes?
On arrival to Indonesia, you'll be asked to complete a customs form. That form asks if you have:
Goods purchased/obtained abroad and will remain in Indonesia with total value exceeding USD 50.00 per person (for Crew) or USD 250.00 per person or USD 1,000.00 per family (for Passenger)
So from that standpoint, you would only need to declare it if you have more than the limit of goods in total, depending on what else you're bringing with you. You're also required to declare commercial articles, so you would need to declare it if it's not a personal effect (e.g. if you're going to sell it or you're a vacuum cleaner salesperson bringing it as a demonstration).
However, a vacuum cleaner is often a large and heavy item. I'd make absolutely sure you are within the baggage limits for your flight, as any excess baggage fees could easily be more than the thing is worth. It's also possible that it could attract some scrutiny from customs or airport security, as they're often interested in anything that seems out of the ordinary.