tpa-rfc-80: update cost estimates

policy/tpa-rfc-80-debian-trixie-upgrade-schedule.md

@@ -360,8 +360,45 @@ retirement ([TPA-RFC-78][]) but is still planned as normal above.
 
 # Costs
 
-The entire work here should consist of about four weeks of work,
-medium uncertainty.
+| Task              | Estimate | Certainty | Worst case |
+|-------------------|----------|-----------|------------|
+| Automation        | 20h      | extreme   | 100h       |
+| Installer changes | 4h       | low       | 4.4h       |
+| Batch 1           | 20h      | low       | 22h        |
+| Batch 2           | 60h      | medium    | 90h        |
+| Batch 3           | 20h      | high      | 40h        |
+| Cleanup           | 20h      | medium    | 30h        |
+| **Total**         | 144h     | ~high     | ~286h      |
+
+The entire work here should consist of over 140 hours of work, or 18
+days, or about 4 weeks full time. Worst case doubles that.
+
+The above is done in "hours" because that's how we estimated batches
+in the past, but here's an estimate that's based on the [Kaplan-Moss
+estimation technique][].
+
+[Kaplan-Moss estimation technique]: https://jacobian.org/2021/may/25/my-estimation-technique/
+
+| Task              | Estimate | Certainty | Worst case |
+|-------------------|----------|-----------|------------|
+| Automation        | 3d       | extreme   | 15d        |
+| Installer changes | 1d       | low       | 1.1d       |
+| Batch 1           | 3d       | low       | 3.3d       |
+| Batch 2           | 10d      | medium    | 20d        |
+| Batch 3           | 3d       | high      | 6d         |
+| Cleanup           | 3d       | medium    | 4.5d       |
+| **Total**         | 23d      | ~high     | ~50d       |
+
+This is *roughly* equivalent, if a little higher (23 days instead of
+18), for exmaple.
+
+It should be noted that automation is not expected to drastically
+reduce the total time spent in batches (currently 16 days or 100
+hours). The main goal of automation is more to reduce the likelyhood
+of catastrophic errors, and make it easier to share our upgrade
+procedure with the world. We're still hoping to reduce the time spent
+in batches, hopefully by 10-20%, which would bring the total number of
+days across batches from 16 days to 14d, or from 100 h to 80 hours.
 
 # Approvals required