Maintenance costs are as hard for a stranger to estimate as to what would be actually comfortable for your family.
It starts with what your standards are for seaworthiness, creature comforts, and cosmetics. Then, what shape is the boat in when you buy it vis a vis those standards.
Then, what does it cost where you live to have repairs and maintenance done to those standards? As for DIY, the first issue is what value you put on your time, a lot of folks apparently value their time at 0. Then of course your capability to do the work in the way that meets your standards.
Lastly, you have to have a reserve fund in place for when Something Really Expensive breaks, like an engine or transmission.

Personally, I think if someone has to ask strangers the answer to these questions, to paraphrase JP Morgan, they can't afford it.