@Tracy Scott it's highly dependent on the deal, the type of property and the location.
In addition to the items others have mentioned, here are some of the biggest potential start-up expenses that I study closely before buying a property:
Foundation/structure--this is one of my few "deal breakers", I typically will not purchase a property with significant foundation or structural issues. The costs to fix these problems can be significant, and in some cases, they're not fixable (at least, not without an unlimited budget).
Roof. Replacing a roof is a significant expense, so I look at the age, condition, and quality of the roof closely.
Sewer line. I never buy a property without scoping the sewer line.
Plumbing. The age, type, and condition of the plumbing is a significant factor in whether I'll buy a property, and how much I'm willing to pay.
Electrical. Again, this can be a big expense if you need to make repairs/updates.
HVAC systems & water heater. A new furnace is pricey.
Asbestos and lead based paint. If you need to remove either, it gets pricey.
Meth test--I always do this on any property I'm purchasing.
Vacancy--how long will I have to hold the property and pay its mortgage before I get tenants? How frequently will the tenants turnover, and how difficult will it be to find new tenants after each turnover? ...if the vacancies are frequent or extended, it can be a big expense, so I analyze this thoroughly.
As for house-hacking specific costs, there are things like furniture/appliances/decor for the common areas of the house, costs of screening applicants (like background checks), cost to advertise, the time and effort required to manage a house hack, etc. ...although these expenses are worth consideration, they tend to be much smaller and almost inconsequential compared to the big capex expenses that can come with buying the wrong property (e.g.; you might spend a couple hundred bucks on tenant screening, but a new roof might cost $20k+).
Back when I was house hacking regularly, one of the most significant "costs" was the cost of my time and effort to acquire tenants (which includes all the time and effort of posting ads, responding to inquiries, answering questions, doing viewings, screening applicants, managing tenants once they were in-place, etc.). Over the years, I greatly refined my systems so that tenant acquisition now requires much less of my time and effort. For instance, I created scripts to manage all inquiries, and started using apps to automate the initial screening process, so that instead of typing out a response every time someone texted me (a nightmare), it all became very automated. I refined my screening process so that non-qualified applicants got screened out ASAP with no work on my side. I started charging refundable fees for viewings (which wouldn't work for an apartment complex, but if a stranger wants to walk through my house, they need to have some skin in the game!); doing this greatly reduced the number of non-serious viewings...all this stuff saves me a lot of time and effort (which ultimately saves me money, and allows me to make more money). ...so, I'd suggest studying up on how to streamline your tenant acquisition process--putting in some work up-front on that can save you a lot of time, effort and money in the long run.
Good luck out there!