Castell y Bere, was a larger Welsh castle.

There is some information from that castle which may give some rough clues to your questions.

William de Valence fighting for King Edward I, captured Castelly Bere from Llwelyn's brother, Dafydd ap Gruffydd in 1283.

After defeating Dafydd, the English left 5 Masons and 5 Carpenters at Castell y Bere to expand and strengthen it. Between 1284 and 1290, about 300 pounds was spent building walls, towers, gate towers, chambers, and a Barbican at Castell y Bere.

These defenses did not prove overly strong, as in the next Welsh war in 1294 it is thought likely (not known for sure) that Castell y Bere was taken by the Welsh and burned. It was not rebuilt.

Caergwrle Castle was built between 1277 and 1282 (when it fell into the hands of the English, damaged, and with the well filled in by the retreating Welsh. The castle was perhaps not yet fully completed at this time, which may be why the Welsh abandoned rather than defended it. It was further damaged by fire a year or so later.).

So, if we make the assumption that the smaller Caergwrle Castle took roughly the same amount of effort to build to its uncompleted state as the extensions to Castell y Bere (a very rough assumption); and they took about the same time (6 years to build); then we might make the following very rough estimates:

1. The building of Caergwrle Castle might have employed 5 masons and 5 carpenters (plus other less skilled laborers).

2. It took roughly 6 years to build and cost about 50 pounds per year.

3. If there were no other costs, this would have made the average pay of the skilled workers 5 pounds a year, but there probably were other costs, so their pay would have been less. (2 pounds / year?)

Note: These are very rough estimates.