Valuing hosting accounts for resale can be a bit subjective as this differs on various factors such as
1. Number of customers you have, whether these customers are long-term, paying consistently (then your price value can increase).
2. What kind of quality service you have provided ( If the service has been exceptional, thats another point for quoting high price).
3.Your annual income from these customers.
4.If the new owner wants to transfer hosting to another provider. Is the transfer process is easy then that adds a value too.
Considering this you can quote price. Also on wht you can check for providers who acquire hosting. Checkout this link
https://www.webhostingtalk.com/forumdisplay.php?f=184
I hope you find this helpful