$4 million startup costs.
Let’s say 10,000 people in the area use the service regularly. That works out to $400 per regular user of the service.
Then you have the yearly costs—including the cost of new city employees. Let’s say that’s only $1 million a year. That works out to $100 per regular user of the service.
$400 per person the first year, $100 per person the following years. It doesn’t take much numbers running to realize that it would be cheaper (a lot cheaper) for the city to just give people bicycles and locks.
Essentially, that's what they are doing because these bikes will disappear over time. Portland is just going about it the more expensive route.