And if you convert it to a rental you’ll be facing a $200k taxable gain. 

I don't remember the exact cost when I did it but I remember thinking it was cheaper than expected.I didn't see a comment mentioning that you should just include utilities in the rent and increase it based off that so I'll be that guy.

If you pay two years' worth of property taxes in 2025 (January and December), both payments are deductible on your 2025 return, potentially reducing your taxable rental income significantly.

In some places it is a lot cheaper to rent instead of buying, but in other areas, it is the same (or cheaper) to buy a home. 

Taxable income will jump in 2026 and again in 2027 substantially.I don't follow the 50-100k mistake logic entirely (not to say it isn't the case).

A conventional would be cheaper.

The cost would be about 500k about $250k cheaper than it would be to buy another duplex property in my area.

You have to put 5% down vs 3.5% down, rates are usually higher, but if you have strong credit, your PMI cost can be cheaper than that of FHA loans. 

and soon realized that there was no aviable apartments in or around the same neighborhood for the price that they were looking for. if they wanted cheaper rent?

If the law allows, I will sometimes move the personal items to storage, which is much cheaper than lost rent, so I can clean up the rental and find a new tenant.