If your work is that easy to estimate, it is perilously close to commoditisation and you need to be on the lookout for a new job in the next four or five years.

The only kind of work I've seen that fits that model is garden variety e commerce or basic systems of record, both of which are going the way of the dodo as off the shelf products eat into that space.

Hell, the last job I was doing was trying to commoditise insurance derivatives. I wrote a DSL for building insurance quote flows we sold internationally. That work was hard to predict because the easy work - building simple boilerplate clients - became our commodity rather than our IP.