[salty_biscuits]

You need to start from what sort of accuracy do you need for the task from a business perspective (including what is acceptable in terms of false positives and false negatives). Just back of the envelope stuff. You have a rough idea of the "I copied stuff other people has done rate" and the "I spent few a days mucking about rate". This stuff always follows a logistic curve with time, starting at your first rate and asymptotically going to high 90%. Use this to get a ball park estimate of how long it will take / cost. If the accuracy required is close to 100% you can probably give up straight away. For things like this that I have done in the past, a good mental model has been if it isn't worth "manually automating" the task (i.e. paying someone somewhere to watch a webcam and send the email so you always have the end product and you eventually get labeled data as a byproduct) it might not be worth trying to automate it.