Taxes and insurance can be calculated before you ever look at a house, let alone sign papers. Automatically assuming it’ll double your monthly payment is foolish. I mean, it might—I’m almost certain it wouldn’t, but it might—but that’s still something you can figure out very easily. A phone call to your insurance company and visit to your county tax assessor’s website is all it takes.
As far as maintenance goes, the rule of thumb I’ve heard is to set aside 2% of your home’s value each year for maintenance costs. So, for a $200K home, you’d set aside $4K per year, or about $333 per month. That’s not chump change, but setting aside that money still wouldn’t double most monthly mortgage payments. Using my own house as an example if we were owners we would be setting aside ~$195 per month. That’s about 30% of mortgage and taxes combined.
HOA fees, or as you noted flood insurance (which again, you’ll know before you ever sigh papers whether you’ll need or not) can change these calculations.