Haha :D I would have the same fear if you would pay for the traffic as this project could cause a lot of it :P
But actually you can pay for each hour:
Source
And you can stop the servers immediatly if the costs are getting too high.
I actually do not know what your future goals are, but if this becomes more than a "fun-project" for you and you are going to fund a company you could think about adding google ads between the posts. At least ~2 years ago finance and crypto ads got paid really really good because there are not that much sites available. This paired with some steemit update posts should cover the costs for sure.
Thanks for replying and best regards,