Four years ago I added 103 sq ft second floor 3 piece bath addition above an existing first floor side addition. all said and done without needing a foundation the project came in at just over 60k with medium priced finishes. This included repairing a driveway and yard after construction. Prices have gone up so much since than due to covid.

We hired an architect for a few grand settled on a plan and than sent it to contractors for detailed price estimates. These estimates we paid for as well but the few hundred was subtracted from our project with the company we went with. There was quite a big differential in what our architect thought the project would cost from what our real contractor estimates came in at.

In my area it is hard right now to get contractors in quickly most are booked well into next fall. Sometimes looking for another house that suits your present needs is both the most economical and timely way to proceed. Good luck

Thank you for your advice

First find out if that is even allowed. Check with your city clerk. Talk to your neighbors who did that to their house. If you decide to do that, you'll probably need an architect.

Be sure to consider the disruption during construction. I'd be shocked if you could do this for less than 150k. Your best bet may be to find a house that meets all your needs, even if it needs cosmetic updating.

I have a split. we also don’t have a bathroom on the main floor. We added a third bathroom to the level below.

Its just 6 steps up to the hall bathroom Or six steps down to the other. Only you can judge if a major add on would be worthwhile.